UNDERGROUND  TRANSMISSION 

AND 

DISTRIBUTION 


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UNDERGROUND 

TRANSMISSION    AND 

DISTRIBUTION 

FOR 

ELECTRIC  LIGHT  AND  POWER 


BY 
E.  B.  MEYER 


MEMBER  AMERICAN  INSTITUTE  OF  ELECTRICAL  ENGINEERS;    MEMBER    AMERICAN 
8OCIETT  OF  MECHANICAL  ENGINEERS;  MEMBER  AMERICAN  ELECTRIC  RAIL- 

WAY ASSOCIATION;  MEMBER  NATIONAL  ELECTRIC  LIGHT  ASSOCIATION; 

CHAIRMAN,  N.  E.  L.  A.  COMMITTEE  ON  UNDERGROUND  CONSTRUCTION 
AND  ELECTROLYSIS,    1915-1916 


FIRST  EDITION 


McGRAW-HILL  BOOK  COMPANY,  INC. 

239  WEST  39TH  STREET.     NEW  YORK 


LONDON:  HILL  PUBLISHING  CO.,  LTD. 

6  &  8  BOUVERIE  ST.,  E.  C. 

1916 


COPYRIGHT,  1916,  BY  THE 
McGRAw-HiLL  BOOK  COMPANY,  INC. 


THK      MAPLE      PRESS      V  Cl  R  K      PA 


PREFACE 

The  rapid  growth  of  the  electric  light  and  power  industry 
with  the  resultant  increase  in  the  number  of  overhead  wires, 
has  brought  about  the  policy  on  the  part  of  municipal  authori- 
ties of  compelling  utility  companies  to  operate  their  systems 
underground.  This  has  led  to  the  development  of  a  more  or  less 
specialized  branch  of  electrical  engineering;  it  involves  large 
expenditures  annually  and  gives  rise  to  operating  difficulties 
in  many  cases  not  clearly  understood  by  the  central  station 
engineer. 

While  there  are  various  treatises  which  deal  with  special 
branches  quite  fully,  there  appears  to  be  no  work  which  covers 
the  general  field  of  underground  construction,  transmission  and 
distribution.  The  writing  of  this  book  was  undertaken  by  the 
author  because  of  repeated  requests  from  engineers  engaged  in 
the  construction  and  operation  of  underground  systems,  for 
information  bearing  on  many  of  the  details  of  this  branch  of 
central  station  work. 

In  the  preparation  of  this  volume,  the  author  has  not  included 
such  data  as  can  readily  be  obtained  from  handbooks.  The 
treatment  of  the  subject  assumes  on  the  part  of  the  reader  a 
general  knowledge  of  the  fundamentals  of  electrical  theory. 
The  subject  matter  has  been  treated  from  the  American 
point  of  view,  since  European  practice  differs  considerably  from 
that  followed  in  America,  due  to  the  difference  in  conditions 
under  which  electric  lighting  properties  are  operated. 

A  part  of  the  material  contained  in  this  volume  originally 
appeared  in  the  various  reports  of  the  National  Electric  Light 
Association  Committee  on  Underground  Construction,  on  which 
committee  the  author  has  served  for  the  past  five  years,  and 
acknowledgment  is  hereby  made  to  the  Association  for  per- 
mission to  use  data  from  these  reports. 

The  author  wishes  to  acknowledge  the  assistance  and  ready 
cooperation  of  the  various  cable  manufacturers  and  others  who 
have  contributed  for  publication  much  valuable  information 


349327 


vi  PREFACE 

and  many  photographs  and  cuts,  and  is  indebted  to  Messrs. 
J.  T.  Foster,  H.  S.  Vassar  and  Paul  Liipke  for  valuable  sugges- 
tions received  during  the  preparation  of  the  manuscript. 

E.  B.  MEYER. 

NEWARK,  N.  J., 
November,  1916. 


CONTENTS 

PAGE 

PREFACE   v 

CHAPTER  I 

HISTORICAL 1 

Periods  of  Development — Built-in  Systems — Drawing-in  Sys- 
tems— Present  Forms  of  Construction. 

CHAPTER  II 

PRELIMINARY  SURVEY 19 

Planning  the  System — Maps — Test  Holes — Permits  and  Right-of- 
way — Form  of  Agreement — Regulations. 

CHAPTER  III 

CONDUIT  AND  MANHOLE  CONSTRUCTION 30 

Selection  of  Materials — Installation  of  Conduit — Concrete — Tile 
Duct — Stone  Duct — Fibre  Duct — Manhole  Construction— Sewer 
and  Illuminating  Gas — Sealing  Ducts  in  Manholes — Types  of  Man- 
hole Construction — Building  Manholes  in  Quicksand — Roof  Con- 
struction— Types  of  Covers — Waterproofing  Manholes — Design  of 
Manholes  for  Transmission  and  Distribution — Transformer  Man- 
holes— Concrete  Manhole  Forms — Distribution  Manholes — Cable 
Tunnels — Specification  and  Contract — Form  of  Specification,  Con- 
tract and  Bond — Construction  Costs. 

CHAPTER  IV 

METHODS  OP  DISTRIBUTION 81 

Street  Distribution — Interior  Block  Distribution — Sidewalk  Dis- 
tribution— Duct  Arrangement — Parallel  Routing — Solid  System — 
Service  Connections — Armored-cable  System — Installing  Steel- 
Taped  Street-lighting  Cable — Comparative  Costs  of  Installation. 

CHAPTER  V 

CABLES 102 

General — Terminology — Conductors — Insulating  Wall — Rubber 
Insulation — Paper  Insulation — Varnished  Cambric  Insulation — 
Graded  Insulation — Lead  Covering — Types  of  Cables — Diameter 
and  Length  of  Cables — Fibre  Core  Cables — Transmission  Cables — 
General  Data — Sector  Cable — Submarine  Cable — Specifications, 
General — Rubber  Cable  Specifications — Paper  Cable  Specifications 
— High  Tension  Cable  Specifications — Moisture  in  Cable  Insulation.- 

vii 


viii  CONTENTS 

CHAPTER  VI 

PAGE 

INSTALLATION  OP  GABLES 151 

Handling  Lead  Cables — Choice  of  Ducts — Rodding  Ducts — 
Obstructions  in  Ducts — Drawing-in  Cables — Cable-pulling  Grips — 
Draw  Rope — Drawing  Apparatus — Power  Trucks — Slack — Joint- 
ing Cables — General  Directions  for  Jointing — Jointing  Rubber- 
insulated  Cables — Jointing  Armored  Cables — Paper  and  Cambric 
Tape  Joints — Paper  Tube  Joints — Advantages  of  Paper  Tube 
Joints — Sleeve  Filling  Material — Conducell  Cable  Joint  Insulators 
— High-voltage  Vacuum  Joint — Unit  Package  of  Joint  Material 
— Protection  of  Cables  in  Manholes — Current-carrying  Capacity 
of  Cables — Cooling  Duct  Lines — Connections  to  Overhead  Lines — 
Lightning  Arresters — Splicing  Equipment,  Tools  and  Safety 
Devices. 

CHAPTER  VII 

TESTING  CABLES 227 

International  Electrical  Units — Standardization  Rules — Electrical 
Tests — Insulation  Resistance — Electrostatic  Capacity — Capacity 
of  Testing  Apparatus — Locating  and  Repairing  Cable  Failures — 
Loop  Test — Fault-locating  Equipment — Periodic  High-potential 
Testing. 

CHAPTER  VIII 

DISTRIBUTION  SYSTEMS  AND  AUXILIARY  EQUIPMENT 241 

General — Alternating-current  Distribution — Single-phase  System 
— Two-phase  Systems — Three-phase  Systems — Secondary  Mains — 
Underground  Transformers — Cable  Junction  Boxes — Service  Bus 
— Manhole  Oil  Switches — A.  C.  Network  Protector — Service  Con- 
nections from  Underground  Mains — Armored  Services — Protection 
of  Transmission  Systems — Relays — Current  Limiting  Reactance 
Coils — Selective  Fault  Localizer — Arcing  Ground  Suppressor — 
Grounded  Neutral  Systems — Merz  System  of  Cable  Protection. 

CHAPTER  IX 

ELECTROLYSIS 281 

General — Drainage  Systems — Protective  Coatings — Insulating 
Joints — Protecting  Cable  Sheaths — General  Practice — Coopera- 
tion of  Utilities — Electrolysis  Surveys. 

CHAPTER  X 

OPERATION  AND  MAINTENANCE 296 

Records — Identification  of  Cables — Record  of  Cable  and  Equip- 
ment Failures — Cleaning  Manholes — Care  of  Cables — Bonding 
Cables  in  Manholes — Rules  and  Requirements. 

INDEX  .  309 


UNDERGROUND  TRANSMISSION 
AND  DISTRIBUTION 

CHAPTER  I 
HISTORICAL 

Periods  of  Development. — For  a  number  of  years  after  electric 
lighting  was  first  introduced,  the  distribution  of  current  was 
effected  almost  entirely  by  means  of  overhead  wires  carried  on 
poles.  The  development  in  many  of  the  large  cities  where  the 
early  market  for  electricity  was  found,  proceeded  at  such  a  rapid 
rate  that  it  soon  became  practically  impossible  to  take  care  of 
the  number  and  size  of  feeders  required  for  distribution  by  means 
of  overhead  construction. 

Large  amounts  of  money  had  been  expended  in  attempting 
to  beautify  various  cities,  but  these  improvements  were  offset 
to  a  great  extent  by  the  erection  of  unsightly  overhead  lines. 
To  remedy  this  condition  and  eliminate  the  fire  hazard,  it  was 
realized  by  engineers  that  some  other  form  of  construction  would 
be  necessary. 

When  the  idea  was  first  conceived  of  relieving  the  streets  and 
boulevards  of  the  presence  of  electric  wires,  by  placing  them 
underground,  there  were  few  engineers  who  believed  the  innova- 
tion practicable,  either  from  the  viewpoint  of  service  or  economy. 
The  cry  immediately  arose  that  the  first  cost  of  an  underground 
installation  would  be  prohibitive  and  it  was  firmly  believed  that 
the  efficiency  and  capacity  of  the  wires  would  be  greatly  lessened. 
This  view  was  supported  by  the  failures  which  attended  the  early 
attempts  to  bury  electric  wires. 

The  earliest  recorded  attempt  to  lay  a  cable  in  the  United 
States  for  the  purpose  of  transmitting  an  electric  current  appears 
to  be  that  made  by  Samuel  F.  B.  Morse  on  Oct.  18,  1842.  That 
evening  he  hired  a  boat  at  the  Battery  water  front,  in  New  York, 
and  paid  out  a  reel  of  copper  wire  laboriously  insulated  with 
pitch,  tar  and  rubber,  as  he  was  being  rowed  to  Governor's 
Island.  He  set  up  and  prepared  to  demonstrate  his  electromag- 

1 


2          UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

netic  telegraph  instruments  at  Castle  Garden  and  the  Island  on 
the  following  day.  Only  a  few  signals  had  been  exchanged, 
however,  when  an  anchor  fouled  the  cable,  and  it  was  cut  by 
ignorant-  sailors  who  dragged  it  up.  Thus  this  first  effort  ended 
in  failure. 

After  strenuous  exertion  Morse  secured  from  Congress,  on  the 
last  day  of  the  session,  March  3,  1843,  an  appropriation  of 
$30,000  "to  test  the  practicability  and  efficacy"  of  his  telegraph 
system.  He  decided  on  a  line  from  Washington  to  Baltimore 
and  planned  to  use  underground  construction,  supposing  that 


FIG.  1. — Calvert  and  German  Streets,  Baltimore,  Md.  Before  removal  of 
poles  and  overhead  wires.  (By  courtesy  of  Mr.  Chas.  E.  Phelps,  Chief 
Engineer,  Baltimore  Electrical  Commission.) 

this  method  had  already  been  successfully  used  in  England  by 
Professor  Wheatstone  for  his  indicating  needle  telegraph.  Morse 
figured  on  four  No.  16  copper  wires  covered  with  cotton  and 
insulating  varnish  and  drawn  into  a  lead  pipe.  The  estimated 
cost  was  about  $600  per  mile.  The  cable  was  constructed  under 
the  supervision  of  an  assistant  who  was  supposed  to  carefully 
test  it.  However,  when  part  of  the  cable  had  been  put  down, 


HISTORICAL  3 

it  was  found  to  be  faulty  due  to  charring  of  the  insulation  in  the 
"hot  process"  employed  in  applying  the  lead.  The  assistant 
was  reluctantly  dismissed  and  the  faithful  Ezra  Cornell,  who  took 
his  place,  dexterously  managed  to  smash  the  cable-laying  outfit 
by  skillfully  guiding  the  trenching  plow  against  a  rock,  thereby 
furnishing  a  convenient  excuse  for  the  change  to  overhead 
construction  which  brought  about  the  success  of  the  enterprise. 
The  precedent  thus  established  dominated  future  developments 
for  a  considerable  period.  Lack  of  care  caused  failure  of  under- 
ground construction  in  this  case,  and  the  same  cause  can  probably 
be  held  responsible  for  more  subsequent  failures  than  any  other. 


FIG.  2. — Damage  to  overhead  wires  resulting  from  snow  and  sleet  storm. 

In  the  years  following,  the  use  of  overhead  wires  for  trans- 
mission of  electric  currents  multiplied.  Besides  telegraphic 
communication,  various  signal  systems,  such  as  fire  alarms  and 
police  telegraphs,  district-messenger-call  systems  and  stock- 
ticker  circuits,  were  established.  Beginning  in  about  1876, 
commercial  application  of  the  telephone  entered  the  field,  in- 
creasing the  number  of  overhead  wires  at  a  rapid  rate,  so  that 
when  in  1878  the  first  series-arc  circuits  made  their  appearance 


4         UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

there  was  already  a  conspicuous  tangle  of  wires  strung  indis- 
criminately above  the  public  highways.  The  situation  was 
aggravated  by  the  neglect  of  defunct  enterprises  to  remove  the 
"dead  wires." 

This  abandoned  and  ownerless  equipment  in  combination  with 
poorly  insulated  electric  light  wires  constituted  a  real  menace, 
that  soon  led  to  a  public  outcry  against  further  increase  of  over- 
head wires  and  the  immediate  undergrounding  of  those  already 
in  use. 

Ill-considered  and  impracticable  legislation  was  the  natural 
consequence  of  this  situation. 

A  remarkable  exception  to  the  general  practice  was  the  radical 
departure  from  accepted  methods  made  by  Mr.  Edison  in  the 
introduction  of  his  low-tension  multiple  system. 

As  one  of  the  items  in  Mr.  Edison's  programme  for  the 
development  of  his  "  system, "  we  find  in  Dyer  and  Martin's 
book,  " Edison,  His  Life  and  Inventions,"  the  following: 

"To  elaborate  a  system  or  network  of  conductors  capable  oj  being 
placed  underground  or  overhead,  which  would  allow  of  being  tapped 
at  any  intervals,  so  that  service  wires  could  be  run  from  the  main 
conductors  in  the  street  into  each  building.  Where  these  mains 
went  below  the  surface,  as  in  large  cities,  there  must  be  protective 
conduit  or  pipe  for  the  copper  conductors,  and  these  pipes  must 
allow  of  being  tapped  wherever  necessary.  With  these  conductors 
and  pipes  must  also  be  furnished  manholes,  junction  boxes,  connec- 
tions and  a  host  of  varied  paraphernalia  insuring  perfect  general 
distribution." 

The  development  of  such  a  "system  or  network"  with  all  the 
necessary  accessories  was  accomplished,  and  on  Sept.  4,  1882, 
current  from  the  Pearl  Street  Station  was  turned  into  under- 
ground wires  laid  under  the  streets  of  a  downtown  section  of 
New  York  City,  supplying  225  houses  wired  for  about  5,000 
lamps. 

However,  this  system  was  not  applicable  to  the  high-tension 
series  currents  used  for  arc  lighting  and  the  number  of  overhead 
wires  for  this  purpose  continued  to  increase  until  in  the  congested 
sections  of  the  larger  cities  the  situation  became  unbearable. 

The  general  unsightliness,  the  menace  to  firemen,  the  dangers 
to  the  employees  of  the  companies  and  to  the  public  at  large 
were  too  apparent  to  be  further  ignored.  In  1884  the  New  York 
Legislature  passed  a  law  requiring  the  removal  of  wires  from  the 


HISTORICAL  5 

streets  before  the  first  day  of  November,  1885.  The  physical 
impossibility  of  compliance  with  this  law  and  the  concrete  fact 
that  at  the  date  set  for  their  disappearance  the  overhead  wires 
were  still  very  much  in  evidence  led  to  the  passage  of  another 
act  in  1885  which  provided  "that,  if  no  suitable  place  should  be 
proposed  for  placing  the  said  wires  underground  it  should  be  the 
duty  of  the  said  Board  of  Commissioners  (created  by  this  act) 
to  cause  to  be  devised,  and  made  ready  for  use,  such  a  general 
place  as  would  meet  the  requirements  of  the  said  Acts  of  1884r-5 
and  the  said  Board  should  have  full  authority  to  compel  all  com- 
panies to  use  such  subways  so  prepared. " 

A  great  variety  of  schemes  was  submitted  to  this  Board,  by 
outside  parties,  about  450  in  all,  but  the  electric  light  companies 
generally  opposed  the  placing  of  electrical  conduits  underground, 
claiming  that  it  was  a  physical  impossibility  to  accomplish 
the  feat  successfully,  and  that  in  any  event  the  cost  would  be 
prohibitive. 

Finally  the  Board  entered  into  a  contract  with  a  conduit 
company  and  a  system  of  iron  pipe  conduit  was  put  down  in 
certain  streets  of  the  city.  On  these  streets  the  authorities 
proceeded,  in  1889,  to  cut  down  the  poles  and  to  remove  the  over- 
head wires  and  thus  ruthlessly  compelled  progress  in  underground 
construction. 

In  Europe  the  situation  had  become  acute  before  it  was  felt 
in  this  country,  and  various  methods  were  tried  with  but  little 
success,  including  the  plan  of  running  the  wires  on  supports 
located  on  the  roofs  of  the  buildings. 

In  France  there  was  developed  the  Berthoud-Borel  System 
employing  copper  wires  wrapped  with  cotton  saturated  with 
linseed  oil,  which  had  been  previously  treated  by  heating. 
The  heat  treatment  appears  to  have  made  the  oil  more  stable 
in  character  and  to  have  increased  its  insulating  properties. 

One  of  the  earliest  forms  of  underground  construction  was 
the  trench  system,  in  which  an  attempt  was  made  to  use  the  same 
general  methods  as  were  used  in  overhead  lines.  The  system 
consisted  of  a  closed  trench  in  which  were  placed  conductors, 
either  bare  or  insulated,  fastened  to  insulating  supports. 

Professor  Jacoby,  of  St.  Petersburg,  laid  a  form  of  armored 
cable  consisting  of  cotton-covered  cord,  laid  in  lead  pipe  with 
the  intervening  spaces  filled  in  with  resin.  There  were  many 
attempts  along  similar  lines,  none  of  which  were  successful 


6         UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

until,  with  the  discovery  of  petroleum  in  1856,  paraffine  came  into 
the  market  as  a  cheap  and  satisfactory  insulating  material. 

The  principal  difficulty  seemed  to  be  in  finding  an  insulation 
which  could  be  made  to  adhere  to  the  conductor.  Many  sub- 
stances were  found  which  were  good  insulators  in  dry  places, 
but  there  were  few  which  would  stand  the  acid  and  alkali  fumes 
and  the  ravages  of  sewer  and  illuminating  gas  to  which  the  con- 
ductors were  exposed  when  buried  under  the  streets  of  our  large 
cities. 

Attempt  was  made  to  use  oil  as  an  insulation  for  cables  and 
what  was  known  as  the  Brook's  System,  Fig.  3,  was  employed 
for  a  time  to  some  extent.  It  was  found  that  wires  insulated  with 
resin  and  oil  were  difficult  to  short-circuit,  even  under  a  high 
potential  difference.  Of  course,  no  pure  oil  could  be  used  in 


FIG.  3. — Brooks  system  of  service-box  cable  and  oil  pipe. 

the  construction  of  cable,  even  when  encased  in  lead,  as  in  the 
jointing  process  the  oil  leaked  out  before  the  joint  was  sealed. 
It  was  proposed  to  lay  iron  pipe  for  the  distance  to  be  traversed, 
the  pipes  to  terminate  in  hermetically  sealed  boxes.  Cables 
which  were  carefully  dried  out  to  get  rid  of  the  moisture  and  then 
covered  with  jute  and  boiled  in  oil  were  drawn  into  these  pipes, 
after  which  the  pipes  were  filled  with  oil  so  that  no  moisture  could 
enter.  The  oil  was  kept  under  pressure  by  means  of  a  standpipe 
or  pump,  the  theory  being  that  if  small  leaks  developed  and 
allowed  the  oil  to  escape,  the  pressure  on  the  oil  would  prevent 
the  entry  of  either  air  or  moisture.  In  addition,  insulation 
break-downs  would  be  self-healing. 

However,  it  was  found  exceedingly  difficult  to  obtain  oil 
sufficiently  heavy  for  good  insulation,  and  that  the  pressure 
from  the  standpipe  or  pump  could  not  be  transmitted  for  any 
great  distance. 


HISTORICAL  7 

Experiments  with  this  type  of  construction  were  made  by 
the  Pennsylvania  Railroad  Co.  and  the  Western  Union  Tele- 
graph Co.,  between  Newark  and  Jersey  City,  across  the  salt 
marshes. 

In  England,  a  system  was  developed  by  Johnson  and  Phillips, 
which  gave  satisfactory  service.  In  their  system  the  idea  of 
using  oil  under  pressure  was  abandoned  and  more  attention  was 
paid  to  the  laying  of  pipes  without  leaks,  taking  especial  pre- 
cautions to  seal  the  junction  boxes  and  the  pipe  ends. 

This  system  was  particularly  adapted  for  electrical  lines 
crossing  private  grounds  and  for  long  trunk  lines  in  which  there 
was  little  probability  of  their  being  disturbed  after  laying. 
It  was  very  difficult,  however,  to  keep  this  sj^stem  in  proper  repair, 
as  leaks  in  the  pipe  line  necessitated  the  placing  of  additional 
junction  boxes  which  were  difficult  to  install  without  removing 
the  cable  and  refilling  the  entire  length  of  the  pipe.  Other 
disadvantages  lay  in  the  objection  of  workmen  to  handling  cables 
saturated  with  heavy  oils  and  in  difficulty  in  making  extensions 
or  branch  connections  to  the  system. 

The  failure  to  obtain  an  insulation  which  would  stand  up 
under  moisture  and  other  deteriorating  influences  brought 
about  the  development  of  the  solid  or  built-in  system. 

Built-in  Systems. — Numerous  solid  or  built-in  underground 
systems  using  both  insulated  and  bare  conductors  were  tried  as 
a  substitute  for  overhead  electrical  wires.  The  enormous  expense 
of  making  the  change,  as  well  as  the  utter  lack  of  experience  with 
buried  circuits,  made  this  a  very  difficult  problem  from  the  start, 
and  as  is  usual  in  such  cases,  extraordinary  methods  were  devised 
for  overcoming  the  difficulties. 

In  England,  the  Crompton  System,  Fig.  4,  of  bare  copper 
strips  was  used  quite  extensively.  This  system  used  bare  con- 
ductors supported  at  intervals  on  insulators  and  laid  in  a  specially 
prepared  trench.  The  system  was  tried  in  two  forms:  In  the 
first,  sag  or  strain  bars  were  placed  at  a  suitable  distance  apart. 
These  took  up  most  of  the  strain  and  very  little  came  upon  the 
insulating  supports  which  were  located  about  50  ft.  apart  and 
carried  on  cast-iron  cross-bars.  In  the  other  form  of  this  system, 
no  strain  bars  were  used,  but  the  number  of  supporting  insulators 
was  increased.  In  both  forms,  but  particularly  in  the  latter, 
trouble  was  experienced  due  to  leakage  of  current  to  earth  at  the 


8         UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


insulator  supports,  probably  caused  by  water  leaking  along  the 
support  and  reaching  the  conductor. 

The  system,  in  both  its  forms,  was  abandoned  because  of  the 
high  cost  of  construction  and  maintenance  and  because  of  inher- 
ent defects,  due  principally  to  the  following: 


FIG.  4. — Section  of  Crompton  and  Kennedy  conduit. 

1.  Temperature  changes  caused  buckling  of  the  strips,  result- 
ing in  heavy  short-circuits  and  interruptions  to  service. 

2.  Lack  of  efficient  drainage  and  ventilation  which  caused 
leakage  of  current  due  to  moisture  and  the  collection  of  gases 

in  the  trench.  Arcing  at  a  poor 
connection  ignited  these  gases,  caus- 
ing disastrous  explosions. 

3.  Heavy  short-circuits  set  up 
electromagnetic  forces  between  con- 
ductors, causing  them  to  buckle  and 
communicate  the  trouble  by  com- 
ing into  contact  with  other  circuits. 
What  is  known  as  the  Callender 
Solid  System,  Fig.  5,  consisting  of 
a  series  of  cast-iron  troughs  laid 
along  the  bottom  of  a  trench,  was 
also  used  to  some  extent.  The  re- 
quired number  of  insulated  conductors  were  strung  in  a  cast-iron 
trough.  After  stringing  the  conductors,  the  trough  was  filled  with 
an  asphalt  compound  and  closed  with  cast-iron  covers.  Experi- 
ments were  carried  on  with  other  forms  of  cast-iron  troughs,  some 
of  which  were  made  in  short  sections  and  bolted  together,  the  cable 


FIG.  5. — Section  of  Callender 
system. 


HISTORICAL  9 

being  placed  in  the  troughs  as  laid .  The  troughs  were  usually  filled 
with  some  kind  of  compound  to  exclude  moisture.  These  methods 
of  providing  underground  distribution,  however,  were  so  expen- 
sive as  to  be  almost  prohibitive.  Moreover,  all  systems  which  em- 
ployed tarry  or  bituminous  filling  had  two  serious  disadvantages. 
It  was  difficult  to  keep  them  rigid  under  all  conditions  of  tem- 
perature, as  at  high  temperatures  the  softening  of  the  material 
caused  sagging  of  the  system  under  the  weight  of  the  earth  above, 
resulting  in  damage  to  both  the  ducts  and  the  wires  which  they 
carried.  At  the  low  winter  temperatures  the  conduit  was  likely 
to  crack  and  admit  moisture.  The  second  disadvantage  lay 
in  the  fact  that  in  making  extensions  to  the  system  it  was  neces- 
sary to  tear  up  the  street  to  get  at  the  cable  on  which  work  was  to 
be  done. 

The  first  objection  was  finally  overcome  by  the  use  of  iron 
pipe  filled  with  compound  to  give  the  necessary  rigidity,  but  the 
second  was  an  inherent  defect  and  was  to  a  large  extent  respon- 
sible for  the  final  abandonment  of  the  built-in  system. 

In  the  early  eighties,  the  Edison  Tube  System  of  underground 
construction  was  devised  and  later  commercially  adopted  by  a 
number  of  the  larger  cities  in  the  United  States  and  Europe. 

This  system  consists  of  20-ft.  lengths  of  iron  pipe  inside  which 
the  conductors  are  embedded  in  a  bituminous  compound.  The 
conductors,  which  are  not  removable,  are  usually  in  the  shape  of 
round  copper  rod,  the  main  tubes  being  designed  for  use  on  the 
three-wire  system.  Each  rod  is  wound  with  a  layer  of  rope  which 
serves  to  keep  the  rods  separated  in  case  a  softening  of  the  insu- 
lating material  in  the  tubes  should  occur.  After  the  rods  have 
been  provided  with  the  layer  of  rope,  they  are  bound  together 
by  means  of  a  wrapping  of  rope  and  inserted  in  the  iron  pipe, 
the  rods  projecting  for  a  short  distance  at  each  end.  The  whole 
tube  is  then  filled  with  an  insulating  compound  which  becomes 
hard  when  cold.  The  20-ft.  lengths  are  made  in  various  sizes 
of  conductors  from  No.  1  gage  up  to  500,000  cm.  for  mains,  and 
1,000,000  cm.  for  feeders.  Sections  of  the  tube  are  designed 
for  use  as  distributing  mains,  and  are  made  with  three  conductors 
of  the  same  size,  while  those  designed  for  feeders  are  often  made 
with  one  conductor  about  half  the  area  of  the  others.  This 
small  conductor  is  used  as  the  neutral  for  which,  in  a  balanced 
system,  little  capacity  is  required.  Tubes  are  also  provided 
with  potential  leads  to  indicate  at  stations  or  substations  the 


10       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

voltage  at  the  outer  end  of  the  feeder.  The  tubes  are  laid  in 
the  ground  about  30  in.  below  the  surface  of  the  pavement  and 
are  joined  together  by  means  of  coupling  boxes.  The  conductors 
are  connected  together  by  means  of  short  flexible  copper  cables 
provided  with  lugs  to  fit  over  the  rods  and  soldered  in  place. 
The  coupling  boxes  are  made  in  two  similar  halves.  After  being 
placed  in  position  the  two  sections  are  securely  bolted  together 
by  means  of  flanged  bolts.  After  this  is  done,  melted  compound 
is  poured  through  an  opening  in  the  upper  casting  and  the  joint 
completed.  Branch  connections  are  made  with  T  coupling  boxes 


FIG.  6. — Edison  tube  coupling  joint. 

which  are  filled  with  compound  in  a  similar  manner.  At  centers 
of  distribution  junction  boxes  are  provided  at  which  the  main 
feeders  and  the  supply  wires  from  the  station  join.  The  junc- 
tion boxes  are  provided  with  fuses  and  water-tight  covers  to 
allow  inspection  and  testing.  When  trouble  occurs,  the  usual 
method  of  procedure  is  to  dig  a  hole  at  one  of  the  couplings  and 
separate  the  ends.  By  making  a  number  of  breaks  in  this  way 
at  different  locations,  the  section  in  which  the  ground  or  short- 
circuit  occurs  is  located  and  the  defective  length  of  tube  replaced. 
The  Edison  System  remained  standard  for  low-tension  distribu- 
tion for  about  15  years,  when  cables  drawn  into  ducts  began  to  be 
employed  for  the  heavy  feeders.  It  is  still  used  to  some  extent 
in  cities  where  a  large  investment  had  been  made  for  such  work 
before  the  development  of  the  drawing-in  system. 


HISTORICAL  11 

In  some  instances,  especially  in  European  countries,  armored 
cables  laid  directly  in  the  earth  have  been  employed  for  under- 
ground distribution.  The  armor,  which  is  in  the  form  of  a  steel 
wire  or  tape,  is  relied  upon  for  mechanical  protection.  This 
form  of  installation  which  is  used  quite  extensively  at  the  present 
time  has  advantages  for  certain  purposes,  as  described  elsewhere 
in  this  volume.  However,  the  ease  with  which  repairs  may  be 
made  in  the  drawing-in  systems  has  caused  these  systems  to 
become  standard  throughout  the  United  States. 


FIG.  7. — Edison  tube  junction  box. 

Drawing-in  Systems. — With  the  development  of  the  alternat- 
ing-current system  of  distribution  and  the  use  of  high-potential 
circuits  of  from  1,000  to  7,000  volts  for  street-lighting  circuits, 
the  need  was  felt  for  some  form  of  insulation  sufficiently  flexible 
to  permit  of  drawing  cables  into  the  ducts.  The  built-in  system 
had  been  abandoned  to  a  large  extent  because  of  its  failure  to 
stand  high  potential  and  because  it  was  found  necessary  to  dig 
up  the  streets  when  increased  load  demanded  reinforcements  or 
additions.  The  constant  tearing  up  of  the  pavement  for  these 
purposes  created  an  antagonistic  feeling  on  the  part  of  the  munici- 
pal authorities  and  in  many  cases  they  were  reluctant  to  grant 
permits  for  the  laying  of  additional  conductors  in  the  streets. 


12       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

In  the  early  forms  of  drawing-in  systems  the  chief  difficulty 
appears  to  have  been  the  lack  of  an  insulating  material  capable 
of  withstanding  the  high  potential  of  arc  circuits.  Some  trouble 
was  also  experienced  on  account  of  disintegration  of  the  lead 
sheath  itself. 

Lead-covered  cables  were  being  operated  successfully  at  low 
voltages,  but  with  the  undergrounding  of  arc-light  wires  failures 
of  the  insulation  soon  resulted. 

The  difficulties  which  were  experienced  in  the  early  days  of 
the  drawing-in  system  were  due  not  to  the  fact  that  the  under- 
ground system  was  fundamentally  wrong,  but  rather  to  the  fact 
that  in  cable  manufacture  lack  of  experience  prevented  the  intel- 


JO1NT. 


FIG.  8. — Dorset  conduit. 

ligent  design  of  the  subsurface  structure  which  was  to  carry  the 
conductors. 

The  problem  resolved  itself  into  three  parts: 

1.  The  insulation  of  the  conductors. 

2.  The  protection  of  the  insulation  from  the  effects  of  moisture 
and  corrosion. 

3.  The  protection  of  both  conductors  and  insulation  from 
mechanical  injury. 

Elaborate  experiments  were  conducted  with  all  kinds  of  cable 
and  with  a  variety  of  conduits,  but  it  was  found  that  copper 
conductors  insulated  with  any  of  the  compounds  which  had 
thus  far  been  tried  failed  under  high  potential  within  a  short 
time.  Where  lead  was  used  to  protect  the  insulation  the  life 
of  the  cable  was  materially  increased. 


HISTORICAL  13 

The  Dorsett  Conduit  System  which  consisted  of  sections  of 
duct  made  with  bituminous  concrete  was  at  one  time  largely 
used  in  New  York  and  Minneapolis  and  proved  a  complete  failure 
on  account  of  the  fact  that  it  was  impossible  to  make  sure  that 
the  compound  between  the  ducts  effected  a  thorough  cementing 
and  in  consequence  after  construction  the  blocks  were  frequently 
found  to  have  cracked  apart  and  fallen  out  of  alignment,  thus 
sacrificing  all  the  insulating  properties  and  reducing  the  cross- 
section  of  the  duct. 

This  type  of  construction  was  somewhat  modified  by  General 
Webber,  of  the  British  Postal  Telegraph  Co.,  and  he  was  able 
to  construct  a  satisfactory  cable-carrying  conduit,  but  could  not 
make  the  system  entirely  waterproof. 

In  Webber's  System,  the  4-in.  or  5-in.  space  between  ducts 
was  filled  with  the  same  material  of  which  the  ducts  were  formed 
in  a  molten  state.  This  molten  material  melted  enough  of  the 
conduit  surface  to  form  the  whole  into  a  solid  mass.  The  system, 
however,  did  not  permit  of  the  use  of  uninsulated  wires. 

The  system  used  in  Minneapolis  by  the  Interior  Conduit  Co. 
consisted  of  impregnated  paper  tubes  with  paper  ferrules  at  the 
joint  laid  in  a  trench.  The  trench  was  filled  with  a  compound 
composed  of  asphaltum  and  coal  tar,  poured  while  hot,  entirely 
covering  the  paper  tubes.  Bare  copper  wires  were  drawn  into 
the  ducts  and  manholes  were  provided.  These  consisted  of 
double  wooden  boxes  sealed  with  compound  and  covered  with 
water-tight  covers.  The  system  worked  well  for  several  years, 
but  was  finally  abandoned  because  of  the  original  use  of  unsatis- 
factory material.  The  paper  ducts  were  found  to  be  not  abso- 
lutely impervious  to  moisture  and  as  the  supporting  wooden 
blocks  in  time  became  saturated  with  moisture  which  seeped 
through  the  paper  conduits,  short-circuits  were  frequent.  The 
installation  was  not  water-tight  and  in  many  instances  the  whole 
duct  structure  was  filled  with  water  after  heavy  rains. 

The  Interior  Conduit  Co.  later  used  a  system  of  paper  tubes 
one  within  the  other,  designed  to  be  laid  with  broken  joints. 
The  tubes  were  protected  externally  by  an  iron  pipe  or  laid  in 
asphaltic  concrete  supported  on  blocks  of  earthenware.  Iron 
manholes  were  substituted  for  the  double  wooden  boxes  used  in 
the  earlier  systems. 

Another  system,  known  as  the  Gumming  Duct,  was  used  to 
some  extent.  Four  wooden  ducts  were  enclosed  in  an  iron  pipe, 


14       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

the  intervening  space  being  filled  with  an  asphaltic  compound. 
This  system  was  limited  to  the  use  of  low-potential  conductors 
where  a  small  number  of  cables  were  installed. 

In  Milwaukee,  three  systems  were  tried  and  abandoned: 
namely,  a  wooden-trench  plan,  tarred  iron  pipe,  and  grooved 
wood.  In  Detroit,  the  Thomson-Houston  Co.  employed  a  cable 
of  the  most  expensive  and  approved  character  in  the  Dorsett 


FIG.  9. — Types  of  wooden  duct.* 


conduit,  and  the  mechanical  work  was  of  the  best  quality.  The 
conduit  was  made  of  a  so-called  concrete  consisting  of  asphal- 
tum  and  sand  moulded  into  3J^-ft.  lengths,  with  the  desired 
number  of  ducts.  One  end  of  each  section  was  flanged  and  two 
sections  were  jointed  and  fitted  together  by  means  of  hot  concrete, 
the  manholes  being  made  of  the  same  material.  In  this  installa- 
tion it  was  found  that  while  the  cables  were  new  the  results  were 


HISTORICAL 


15 


fair,  but  the  loss  by  leakage  rendered  it  impossible  to  provide 
proper  voltage  regulation  at  the  lamps. 

Creosoted  wood,  or  what  is  commonly  known  as  pump-log 
conduit,  was  used  in  a  number  of  installations.  This  conduit 
though  cheap  was  found  to  deteriorate  very  rapidly  and  to  cause 
much  trouble  by  catching  fire  when  a  cable  burnout  occurred. 
In  many  installations  the  decay  of  the  wood  formed  acetic  acid 
which  attacked  the  lead  sheathing  of  the  cable.  As  the  result 
of  these  difficulties  the  use  of  wood  as  a  conduit  was  soon 
abandoned. 

Cement-lined  pipe  was  largely  used  about  15  years  ago.  This 
consisted  of  sections  of  thin  wrought-iron  pipe,  No.  26,  B.W.G., 
0.018  in.  thick,  securely  held  by  rivets  2  in.  apart.  The  tube  was 


RIVCTS 

/& 

•pJ  *~* 

3" 

HH^I  -.Wv^ffi:.:^S 

//POM 

FIG.  10. — Details  of  cement-lined  pipe. 

lined  with  a  wall  of  Rosendale  cement  %  in.  thick,  the  inner  sur- 
face of  which  was  polished  while  drying,  so  as  to  form  a  perfectly 
smooth  tube.  The  ends  of  the  tubes  were  provided  with  a  cast- 
iron  beveled  socket  joint  to  obtain  perfect  alignment.  The 
cement  lining  in  this  form  of  conduit,  after  several  years  service, 
separated  from  the  outer  iron  form,  causing  considerable  trouble 
in  the  installation  and  withdrawal  of  cables.  In  some  cases  the 
cement  lining  was  porous  and  with  the  absorption  of  moisture 
the  conduit  soon  disintegrated  so  that  this  form  of  construction 
had  a  very  short  life. 

Wrought-iron  or  steel  pipes  screwed  together  by  means  of 
couplings  were  used  for  a  number  of  years,  particularly  where 
the  high  cost  was  not  a  serious  objection.  Wrought-iron  pipe 
laid  up  in  cement  and  additionally  protected  with  2-in.  plank 
was  for  a  long  time  considered  standard  construction  in  New  York 


16       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


City.  Its  special  advantages  are:  great  strength  to  resist  the 
severe  strains  caused  by  the  pressure  of  the  earth,  and  that  it 
is  well  adapted  to  withstand  blows  from  workmen's  shovels  and 
tools,  to  which  conduits  in  large  cities  are  subjected  because  of 
the  frequency  of  street  excavation  work.  The  pipes  are  standard 
3-in.  and  4-in.  diameter  and  are  made  gas-  and  water-tight  by 
means  of  a  tapering  screw-thread  coupling.  The  pipes  are  laid 
about  an  inch  apart  and  the  spaces  around  them  filled  with  con- 
crete. It  is  evident  that  this  form  of  construction  is  extremely 


>.          -    •          •-   o     • 
•*~  •  "-.•'  *V4'-».  '»'•'«'  *;>~ 


,',  "  ^ 
o  _ 

&  'o 


^^^^8^<S^ 


*>v*  '*.«•'  *."*••*•''•  -'i  ^2 


FIG.  11. — Cross-section  of  iron-pipe  conduit. 

substantial  and  will  withstand  the  most  severe  mechanical 
stresses,  but  because  of  its  high  first  cost  it  has  been  superseded 
by  cheaper  systems. 

In  the  city  of  Paris,  the  sewers,  which  are  egg-shaped  in  form, 
are  purposely  constructed  much  larger  than  necessary  for  carry- 
ing sewage,  so  that  the  upper  portion  may  be  rented  for  pipe  and 
conduit  lines.  Service  connections  are  made  through  the  sewer 
pipes  connected  to  each  house,  thus  avoiding  the  use  of  manholes. 
The  sewers  are  large  enough  to  allow  a  man  to  stand  upright, 
while  the  main  sewers  are  often  27  ft.  in  diameter.  Perforated 
manhole  covers  are  provided  at  intervals  to  allow  for  ventilation 
and  give  access  for  cleaning.  The  air  in  the  sewers  is  fresh, 


HISTORICAL  17 

although  a  slight  musty  odor  associated  with  sewage  is  notice- 
able. Gas  mains  are  not  carried  in  the  sewers  as  they  are  con- 
sidered a  danger  on  account  of  the  possibility  of  an  explosion. 
Electric  service  connections  are  carried  through  the  individual 
service  connections  to  the  buildings. 

Present  Forms  of  Construction. — Tile  and  fiber  conduits  are 
now  used  almost  exclusively.  The  first  is  manufactured  from 
vitrified  clay  in  single  duct  and  multiples  of  two,  three,  four  and 
six  ducts,  in  either  round  or  square  bore.  The  ducts  are  laid 
end  to  end  and  usually  surrounded  with  an  envelope  of  concrete 
which  reinforces  the  structure.  The  joints  are  staggered  and 
wrapped  with  either  burlap  or  iron  and  covered  with  cement. 

While  there  is  some  difference  of  opinion  among  engineers  as 
to  which  type  of  conduit  is  the  better,  the  clay-duct  system  is 
more  generally  used  in  distribution  work.  The  newer  material, 
known  as  fiber  conduit,  is  rapidly  coming  into  general  favor,  and 
at  present  is  considered  standard  construction  and  used  success- 
fully by  a  number  of  the  larger  companies. 

In  some  locations  stone  pipe  is  being  used  to  advantage  and 
its  cost  compares  favorably  with  that  of  tile  and  fiber  conduit. 
An  ideal  conduit  would  provide  absolute  protection  for  the 
cables  from  every  destroying  influence.  It  should  be  proof 
against  acids,  alkalies,  gases  and  all  other  chemical  elements; 
it  is  likewise  essential  that  it  be  non-corrosive  and  absolutely 
permanent  in  character  and  composition;  it  should  also  have 
high  insulating  qualities  to  protect  the  cables  from  outside  cir- 
cuits and  avoid  electrolysis.  The  joints  should  be  self -aligning 
and  insure  permanently  fixed  alignment,  and  the  duct  should 
have  a  hole  with  a  smooth  and  strictly  non-abrasive  inner 
surface,  to  entirely  prevent  injuries  to  the  covering  of  cables 
while  drawing  them  in  and  out  of  the  ducts.  The  ducts  should 
be  light  in  weight  to  save  expense  in  freighting,  handling,  and 
laying,  and  should  be  strong  and  tough  for  proper  protection  of 
cables  and  to  avoid  loss  from  breakage,  in  shipping  and  handling, 
and  lastly  the  first  cost  should  not  be  excessive. 

It  is  a  well-established  fact  that  when  a  system  is  properly 
designed,  the  saving  in  the  cost  of  maintenance,  the  increase 
in  efficiency,  the  superior  service  and  absolute  insulation,  in  a 
very  short  time  unquestionably  repay  for  the  increased  first 
cost.  The  cost  of  the  subsurface  structures  among  the  larger 
central-station  companies  may  be  said  to  amount  to  one-fourth 


18       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

of  the  entire  investment,  and  for  the  reason  that  these  structures 
are  themselves  as  important  as  any  link  in  the  chain  of  central- 
station  equipment,  and  because  of  the  relatively  large  investment 
involved,  great  care  should  be  exercised  in  determining  the  kind 
and  type  of  underground  construction  to  be  used.  In  the  suc- 
ceeding chapters  the  types  of  construction  which  are  in  use  to-day 
are  described  in  detail,  together  with  specifications,  costs,  and 
other  data  to  be  used  as  a  guide  for  the  central-station  engineer 
in  the  design  and  operation  of  underground  systems  of  trans- 
mission and  distribution. 


CHAPTER  II 
PRELIMINARY  SURVEY 

Planning  the  System. — In  planning  a  conduit  system  for 
general  use  in  housing  both  transmission  and  distribution  feeders, 
as  well  as  mains  and  service  cable,  the  first  thing  to  be  decided 
upon  is  the  method  of  distribution.  The  system  of  distribution 
depends  to  a  large  extent  upon  local  conditions  and  in  many  cases 
will  follow  the  general  plan  of  the  existing  overhead  system,  except 
in  large  cities  where  obstructions  in  the  streets  and  the  expense 
of  approved  paving  methods  will  frequently  determine  to  a  great 
extent  the  route  to  be  followed. 

In  some  cities,  local  ordinances  prescribe  the  use  of  poles  in 
alleys  for  block  distribution,  and  in  such  cases  the  conduits  are 
usually  laid  on  the  main  streets  or  thoroughfares.  Where  the  use 
of  overhead  alley  distribution  is  permissible,  the  problem  of 
eliminating  pole  lines  from  the  streets  is  relatively  easy  and  the 
cost  of  underground  construction  is  materially  reduced. 

Maps. — When  the  method  of  distribution  has  been  decided 
upon  and  the  streets  on  which  the  ducts  are  to  be  laid  have  been 
determined,  a  map  should  be  prepared  showing  the  location  and 
size  of  the  proposed  duct  line. 

The  problems  presented  to  the  engineer  who  is  responsible 
for  the  installation  of  an  underground  system  are  many,  but  he 
has  a  comparatively  large  field  from  which  to  choose  methods  and 
materials.  Local  conditions  will  determine  to  a  large  extent  the 
character  of  the  construction  to  be  employed.  Conduit  systems 
are  usually  laid  subsequent  to  other  subsurface  structures  such 
as  water  and  sewer  pipes  and  gas  mains,  and  it  is  therefore  neces- 
sary in  preparing  specifications  and  estimates  that  locations  of 
existing  subsurface  structures  be  known  in  advance  as  definitely 
as  possible.  The  engineer  should,  therefore,  provide  himself 
with  a  map  of  the-  district  to  be  covered  in  order  that  he  may 
determine  what  streets  can  best  be  used  after  considering  the  load 
on  the  system  and  determining  the  method  of  distribution.  Maps 
or  surveys  should  be  drawn  to  scale  in  order  that  the  locations 
of  foreign  structures  may  be  plotted  thereon. 

19 


20       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

A  record  of  the  subsurface  structures  can  generally  be  obtained 
by  applying  to  the  municipal  authorities.  While  this  informa- 
tion will  frequently  be  found  of  great  value  in  making  a  pre- 
liminary layout,  too  much  dependence  should  not  be  placed 
thereon,  as  such  records  are  not  always  accurate  and  are  quite 
often  incomplete. 

It  is,  therefore,  necessary  to  check  up  these  records  in  the  streets 
where  underground  structures  are  numerous,  particularly  in 
cases  where  the  space  available  for  a  conduit  installation  is  limited 
by  such  structures. 

Test  Holes. — Obstructions  are  most  likely  to  be  encountered 
at  street  intersections,  and  these  obstructions  should  be  located 
as  accurately  as  possible  before  beginning  the  trench  excavation. 


FIG.  12. — Method  of  building  manhole  around  obstructions. 

It  is  best  to  find  obstructions,  such  as  water  and  gas  mains 
and  the  service  connections  of  other  utilities  by  digging  test  holes 
along  the  line  of  work,  and  so  laying  out  the  work  as  to  avoid 
them  when  possible. 

These  test  holes  are  usually  about  2  ft.  in  width,  extend  from 
curb  to  curb  and  are  of  sufficient  depth  to  show  the  locations  of 
the  lowest  structures.  Only  one-half  of  the  street  is  opened  at 
one  time  in  order  not  to  interfere  with  traffic.  To  determine 
definitely  that  the  proposed  location  of  the  conduit  line  is  clear 
of  other  underground  structures  and  obstructions,  these  test 
holes  should  be  dug  at  intervals  along  the  line  far  enough  in 
advance  of  the  trench  so  that  any  errors  in  records  of  previous 
work  in  the  streets  or  in  the  location  of  the  conduit  line  will  be 
disclosed  before  incurring  the  expense  of  digging  the  trench. 


PRELIMINARY  SURVEY 


21 


Where  possible,  test  holes  should  be  dug  at  the  proposed  man- 
hole sites  with  the  double  purpose  of  utilizing  the  extra  excava- 
tion and  of  obtaining  definite  information  as- to  the  availability 
of  the  proposed  manhole  location. 


/Curb 


-Gas 


FIG.  13. — Street  main  cut  around  manhole. 


£P»Ce  AKOUND  f/fC 


FIG.  14. — Method  of  building  conduit  around  service  pipes. 

It  is  frequently  found  after  measurements  are  taken  in  the  test 
holes,  that  while  there  is  sufficient  space  for  the  conduit,  the  space 


22       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

for  manhole  construction  is  so  limited  as  to  make  it  necessary  to 
provide  a  special  form  of  construction.  In  Fig.  12  is  illustrated 
a  method  of  installing  a  manhole  in  a  congested  street  where 
foreign  obstructions  make  it  necessary  to  resort  to  an  unusual 
design.  In  some  cases  it  may  be  cheaper  to  have  the  water 
or  gas  pipes  cut  around  the  manhole  as  shown  in  Fig.  13.  The 
conduit,  when  installed  parallel  to  water  or  gas  mains,  should  be 
placed  at  a  grade  which  will  not  interfere  with  the  water-  or 
gas-service  connections.  But  where  this  is  impossible,  the 
service  pipe  is  usually  run  through  the  conduit,  the  ducts  being 
divided  and  the  space  around  the  service  pipe,  where  it  passes 
through  the  conduit,  filled  with  sand,  as  shown  in  Fig.  14.  Gas 
mains  should  not  be  run  through  manholes  except  only  in  very 
special  cases.  Where  it  is  necessary  to  take  a  gas  main  into  a 
manhole,  it  should  be  encased  in  concrete. 

Permits  and  Right-of-way. — Before  proceeding  with  any 
actual  construction  work  in  the  streets,  the  engineer  should 
acquaint  himself  with  the  local  municipal  laws,  ordinances  and 
regulations  or  other  requirements  relating  to  the  excavation  or 
the  occupancy  of  space  in  the  public  streets.  Notes  as  to  ob- 
structions or  any  other  points  relating  to  the  work  should  be 
made  and  arranged  in  a  form  convenient  for  reference. 

In  some  cities  pavements  are  laid  by  contractors  under  bond 
with  the  municipal  authorities  to  keep  such  pavements  in  good 
repair  for  a  period  of  years.  In  such  cases  it  is  usually  necessary 
to  restore  the  pavement  after  street  excavations  have  been  made. 
In  many  instances  it  is  impossible  to  obtain  permits  for  street 
opening  after  a  new  pavement  has  been  installed,  and  this  should 
be  given  consideration  in  laying  out  a  route  for  the  conduit  system, 
as  it  has  often  been  found  advisable  to  install  a  conduit  system 
in  advance  of  the  laying  of  a  permanent  pavement  in  order  to 
keep  the  cost  within  reasonable  limits. 

The  engineer  should  confer  with  the  local  authorities  in  the 
matter  of  obtaining  permits  for  the  opening  of  streets,  the  use  of 
fire  hydrants  and  the  methods  of  obtaining  permits  and  the  rates 
of  payment  for  water  used  for  construction  purposes. 

In  many  European  cities  it  is  the  practice  to  install  the  subsur- 
face structures  of  the  utilities  beneath  the  sidewalk.  Regulations 
are  in  force  prescribing  the  exact  location  beneath  the  sidewalk 
within  which  each  utility  must  be  placed.  In  some  places  a 
movable  pavement  is  provided  which  may  be  removed  and  re- 


PRELIMINARY  SURVEY  23 

placed  without  great  expense,  allowing  repairs  to  be  made  to  the 
subsurface  structures.  The  advantages  of  locating  utilities  be- 
neath the  sidewalks  as  compared  with  their  placement  beneath 
the  street  pavement  are  that  it  is  less  expensive  to  remove  a 
cheap  sidewalk  than  a  costly  pavement,  and  the  maintenance 
cost  is  lowered.  Structures  placed  under  the  sidewalk  are  not 
subjected  to  the  shock  and  vibration  from  heavy  overhead 
traffic,  and  the  installation  of  transportation  subways  is  made 
considerably  less  expensive  where  no  underground  utilities  have 
to  be  maintained  in  service  during  construction. 

In  some  of  the  larger  cities  in  the  United  States,  the  streets 
have  become  so  congested  with  both  surface  and  subsurface 
structures  that  the  matter  of  subsurface  construction  has  been 
placed  under  the  control  of  a  Municipal  Board  consisting  of  the 
Chiefs  of  Bureaus  of  Highways,  Surveys,  City  Property,  Electri- 
cal Bureaus,  etc.,  the  idea  being  to  have  all  departments  concerned 
with  surface  or  subsurface  construction  of  streets  represented 
on  the  Board.  One  of  the  most  important  duties  of  this  Board 
is  the  obtaining,  compiling  and  mapping  of  all  possible  informa- 
tion concerning  existing  or  projected  structures  under  streets. 
For  carrying  out  the  work,  a  corps  of  field  inspectors  and  drafts- 
men is  maintained,  and  necessary  authority  and  power  given  the 
Board  to  enable  it  to  obtain  the  required  information  and  to  con- 
trol the  action  of  both  corporations  and  individuals  in  their 
use  of  the  streets. 

In  some  cities  it  is  required  that  plans  showing  all  existing 
underground  structures  be  filed  in  duplicate  together  with  com- 
plete details  of  proposed  construction.  All  work  and  material 
used  must  be  satisfactory  to  the  Chief  of  the  Electrical  Bureau 
and  any  work  and  material  condemned  must  be  at  once  replaced 
in  acceptable  form.  After  work  is  completed,  the  party  to  whom 
the  permit  is  issued  is  required  to  file  complete  plans  in  detail 
showing  the  work  as  constructed,  with  all  previously  existing 
structures  encountered  during  the  construction  work. 

The  foregoing  applies  to  only  a  few  cases  where  subsurface 
structures  and  transportation  subways  occupy  practically  all 
of  the  available  space  under  the  street  surface. 

When  electrical  companies  are  required  to  remove  overhead 
wires  and  poles  from  streets  or  public  highways,  it  is  the  usual 
practice  to  confer  with  the  authorities  and  arrange  for  some  satis- 
factory manner  of  procedure.  While  franchise  requirements  will 


24       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

govern  the  form  of  the  agreement  in  any  particular  case,  the 
following  is  submitted  as  a  specimen: 


FORM  OF  AGREEMENT 

AN  ORDINANCE  granting  permission  to  (name  of  company),  its  suc- 
cessors and  assigns,  to  lay  and  maintain  underground  conduits,  cables, 
wires  and  manholes  for  electrical  conductors  in  the  streets,  avenues  and  pub- 
lic places  of  the  city  (or  town)  of for  the  use  and  purposes  of  its 

business,  and  providing  for  the  removal  of  certain  overhead  wires  and  pole 
lines. 

BE  IT  ORDAINED  by  the  Common  Council  of  the  city  (or  town)  of  .... 
as  follows : 

SECTION  I. — That  (name  of  company),  its  successors  and  assigns,  be  and 
it  is  hereby  authorized  and  empowered  to  construct  and  maintain  for  the 
use  and  purposes  of  its  business,  a  system  of  subways  and  underground  con- 
duits, laterals,  service  conduits,  service  boxes  and  manholes  beneath  the 
surface  of  the  streets,  avenues,  and  other  public  places  of  the  city  (or  town) 

of as  the  boundaries  thereof  are  now  or  may  hereafter  be,  and  to  place, 

maintain  and  operate  therein  wires,  cables  and  other  electrical  conductors 
necessary  for  such  purposes;  provided  that  said  subway  shall  be  confined 
within  a  space  of  four  (4)  feet  in  width,  except  the  manholes,  which  may  be 
constructed  of  the  usual  size  and  shape  necessary  or  advantageous  for  the 
conduct  of  the  business  of  said  company. 

SECTION  II. — That  (name  of  company)  shall,  within  six  (6)  months  after 
the  passage  and  acceptance  of  this  ordinance,  proceed  to  construct  its  sub- 
ways or  underground  conduits  with  the  necessary  laterals,  service  conduits, 
service  boxes,  manholes  and  street  openings  in  (state  requirements  of  first 
year's  work,  giving  names  of  streets  and  avenues  in  which  conduits  are  to 
be  installed).  After  the  completion  of  the  subways  or  underground  conduits 
in  the  above-mentioned  streets,  said  (name  of  company)  may  extend  its 
conduits  and  subways  through  the  other  streets,  avenues,  and  public  places 

of  the  city  (or  town)  of from  time  to  time,  as  the  requirements  of  its 

business  shall  demand. 

SECTION  III. — That  within  one  year  from  the  laying  of  subways  or  con- 
duits in  any  street,  avenue  or  public  place  in  the  city  (or  town)  of or 

any  section  thereof,  said  company  shall  remove  its  electrical  conductors, 
poles  and  fixtures  from  above  the  surface  of  those  sections  of  said  streets, 
avenues  or  public  places  beneath  which  said  subways  or  conduits  shall  be 
constructed,  except  where  said  poles  and  fixtures  are  used  for  supporting 
public  lights,  or  for  the  purpose  of  supporting  or  connecting  with  wires  in 
intersecting  streets,  and  thereupon  the  right  of  said  company  to  maintain  the 
poles  so  required  to  be  removed  shall  cease  and  become  void;  and  the  said 
company  shall  repair  the  sidewalks  from  which  said  poles  shall  have  been 
removed. 

SECTION  IV.— That  the  said  (name  of  company)  before  opening  any  street 
for  the  doing  of  any  part  of  the  work  hereby  authorized,  shall  from  time  to 
time  file  in  the  office  of  the  city  (or  town)  of a  map  or  plan  showing 


PRELIMINARY  SURVEY  25 

the  proposed  location  and  dimensions  of  the  subways,  underground  conduits 
and  manholes,  or  any  portion  thereof,  proposed  to  be  constructed  in  any 
such  street,  avenue  or  highway,  which  location  or  locations  shall  become 
operative  from  the  time  of  such  filing.  The  said  subway  or  underground 
conduits  shall  be  made  of  (specify  the  kind  and  types  of  construction),  and 
shall  be  laid  not  iess  than  two  (2)  feet  beneath  the  surface  of  the  streets, 
and  not  less  than  one  (1)  foot  outside  of  the  curb  lines,  except  where  neces- 
sary to  avoid  obstructions;  and  shall  conform  to  the  laws  of  the  State  govern- 
ing the  laying  of  subways  for  the  transmission  of  electricity  for  light,  heat 
or  power. 

The  manholes  shall  be  located  beneath  the  surface  of  said  streets  at  such 
points  along  the  line  of  the  subways  or  underground  conduits  as  may  be 
necessary  or  convenient  for  placing,  reaching  and  operating  the  electrical 
conductors  which  the  said  company  may  from  time  to  time  place  in  sub- 
ways or  underground  conduits,  and  shall  be  so  constructed  as  not  to  inter- 
fere with  the  passage  of  the  public  over  and  along  the  said  streets;  and  the 
said  company  shall  restore  such  street  or  avenue  which  may  be  disturbed 
in  the  construction  and  maintenance  of  the  subways,  conduits,  laterals, 
or  manholes  to  the  condition  in  which  it  was  at  the  commencement  of  the 
work  thereon,  and  free  from  any  cost  or  expense  whatever  to  the  city  (or 

town)  of In  backfilling  of  the  trenches,  the  earth  shall  be  put  in 

layers  of  not  more  than  six  (6)  inches  at  a  time ;  it  shall  be  thoroughly  rammed 
and  compacted  before  another  layer  of  dirt  is  placed  thereon,  and  where 
necessary  it  shall  be  carefully  and  thoroughly  puddled.  The  electrical 
conductors  and  conduits  therefor  shall  be  so  placed  as  to  do  no  injury  to  any 
shade  tree  or  to  the  property  of  any  person  or  persons,  or  to  any  public 
or  private  sewer,  or  to  any  water  or  gas  pipe,  or  to  the  wires  or  conduits 
of  any  other  company.  At  least  forty-eight  (48)  hours  before  the  opening 
of  any  street  or  avenue,  the  said  company  shall  notify,  in  writing,  the  city 
(or  town)  engineer  of  the  desire  of  the  said  company  so  to  do,  stating  the 
place  and  purpose  of  such  proposed  opening,  and  the  said  company  and  its 
servants  and  employees,  in  the  laying  of  any  wires  or  conduits,  in  excavating 
and  replacing  the  earth  in  any  street  or  avenue,  and  in  replacing  the  pave- 
ment thereon,  shall  be  under  the  supervision  of  the  city  (or  town)  engineer, 
or  the  proper  officer  appointed  by  him  having  supervision  of  streets  and  high- 
ways. The  earth  removed  in  making  any  excavation  shall  be  restored,  and 
the  pavement  taken  up  and  relaid  by  the  said  company  in  a  thorough  and 
workmanlike  manner,  and  in  such  manner  as  to  prevent  any  future  sinking 
of  the  pavement.  The  pavement  so  disturbed  or  taken  up,  either  in  the 
original  construction  of  said  work  or  in  any  subsequent  repairs  to  the  work, 
shall  thereafter  be  maintained  by  the  said  company  for  a  period  of  one  (1) 
year,  unless  said  street  is  repaved  within  such  time,  in  as  good  condition 
as  the  surrounding  pavement.  No  street,  avenue  or  public  place  shall  be 
encumbered  for  a  longer  period  than  shall  be  necessary.  In  prosecuting 
said  work  not  more  than  one  thousand  (1,000)  feet  of  any  street,  avenue 
or  highway  shall  be  opened  at  one  time,  and  in  all  cases  and  at  all  times  dur- 
ing the  prosecution  of  such  work  in  any  street,  avenue  or  highway,  a  proper 
passageway  for  vehicles  shall  be  kept  open  and  free  at  the  intersection  of 
streets. 


26       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

The  cost  of  restoring  the  earth  or  otherwise  and  the  cost  of  replacing  the 
pavement  and  repairs  thereto,  caused  by  the  opening  of  any  such  street 
or  avenue,  shall  be  paid  for  by  said  company,  and  the  said  company  shall 
likewise  pay  the  cost  of  an  inspector  appointed  by  the  city  (or  town)  of 

to  supervise  the  work.  The  expense  of  such  supervision  and  the  cost 

of  such  inspector  shall  be  paid  by  said  company  upon  the  presentation  of 
bills  therefor,  certified  by  the  proper  officer  of  the  city  (or  town)  and  the 

expense  to  which  the  city  (or  town)  of shall  be  put  from  the  neglect 

of  said  company,  or  its  employees  or  the  doing  of  any  work  in  an  unwork- 
manlike manner  in  the  digging  of  trenches  or  holes,  or  in  the  restoring  of 
the  earth,  or  of  the  relaying  or  replacing  of  any  pavement,  shall  in  like 
manner  be  paid  by  said  company.  In  case  the  work  or  any  part  thereof 
shall  not  be  done  to  the  satisfaction  of  the  city  (or  town)  engineer,  or  the 
person  appointed  by  him  having  the  supervision  of  streets  and  highways, 
the  said  city  (or  town)  engineer  may,  without  waiving  any  of  its  rights 
hereunder,  cause  the  said  work  to  be  performed  or  material  to  be  supplied 
to  its  satisfaction;  and  the  company  agrees  upon  the  presentation  of  bills 
therefor,  certified  by  the  proper  officer  in  the  city  (or  town)  to  pay  at  once 
the  same,  including  the  cost  of  both  inspection  and  of  labor  and  material; 
provided,  however,  that  before  any  work  shall  be  done  or  material  supplied 

by  the  city  (or  town)  of for  the  cost  of  which  (name  of  company) 

under  this  section  shall  be  liable,  the  city  (or  town)  engineer  shall  give 
notice  in  writing  to  (name  of  company)  of  the  work  required  to  be  done  and 
the  material  required  to  be  supplied,  and  the  company  shall  have  ten  (10) 
days  within  which  to  begin  the  work  and  supply  material  by  such  notice 
required  to  be  done  or  provided,  and  shall  have  a  reasonable  time  thereafter 
within  which  to  complete  the  said  work. 

SECTION  V. — The  said  company  shall  indemnify  and  save  harmless  the 

city  (or  town)  of ,  its  officers,  servants  and  agents,  against  all  loss, 

and  shall  assume  all  liability  and  pay  all  damages  which  may  at  any  time 

arise,  come  or  occur  to  the  city  (or  town)  of ,its  officers  or  agents,  from 

any  injury  to  person  or  property,  from  the  doing  of  any  work  hereinbefore 
mentioned,  or  from  the  doing  of  said  work  negligently  or  unskillfully, 
or  from  the  neglect  of  said  company  or  its  employees  to  comply  with  the 

provisions  of  any  ordinance  of  the  city  (or  town)  of relative  to  the 

use  of  the  streets,  or  from  the  failure  to  put  up  proper  lights  and  barriers  at 
or  around  excavations,  or  from  the  failure  to  support  properly  the  tracks  of 
steam  railroads  or  street  railways  during  the  prosecution  of  the  work  and 
thereafter,  and  the  acceptance  by  the  company  of  this  ordinance  shall  be 

an  agreement  by  said  company  to  pay  the  city  (or  town)  of on  any 

sum  of  money  for  which  the  city  (or  town)  of may  become  liable 

from  or  by  reason  of  any  injury  or  damage. 

SECTION  VI. — The  said  company  shall  file  with  the  city  (or  town)  of 

its  acceptance  of  this  ordinance  within  thirty  (30)  days  from  the  date  on 
which  it  shall  take  effect. 

SECTION  VII. — That  the  company  shall  repay  the  city  (or  town)  of 

the  amount  of  the  cost  and  expense  to  the  city  (or  town)  of 

of  all  official  publication  of  this  ordinance. 

SECTION  VIII. — That  this  ordinance  shall  take  effect  immediately. 


PRELIMINARY  SURVEY  27 

Other  forms  of  agreement  provide  for  the  removal  of  overhead 
wires  and  poles  in  certain  definitely  prescribed  sections  of  the  city 
or  town,  covering  a  period  of  from  5  to  20  years.  In  such  cases 
the  operating  company  has  the  advantages  of  being  in  a  position 
to  lay  out  definitely  its  work  from  year  to  year,  and  to  make 
plans  for  the  entire  system,  thus  providing  at  the  very  start  for 
the  ultimate  number  and  size  of  conduit  and  manholes. 

Still  other  forms  of  agreement  provide  for  the  expenditure  of 
a  certain  sum  ranging  from  $5,000  to  $50,000,  depending  on 
the  size  of  the  city  and  the  financial  condition  of  the  operating 
company. 

Some  companies  have  agreed  to  construct  each  year  a  certain 
number  of  lineal  feet  of  underground  conduit,  the  municipality 
exercising  the  right  to  designate  the  streets  in  which  it  desires 
to  have  conduit  installed,  covering  not  more  than  one-half  of 
the  total  amount,  the  remainder  being  left  to  the  judgment  of 
the  company.  The  streets  designated  by  the  city  (or  town)  must 
be  contiguous  to  the  present  subway  system.  The  forms  of 
agreement  regarding  the  amount  of  work  to  be  done  are  de- 
pendent entirely  on  local  conditions,  and  the  foregoing  outline  is 
given  merely  to  aid  the  engineer  in  determining  a  proper  method 
of  procedure. 

Regulations. — Many  states  have  enacted  laws  to  regulate  the 
construction  and  maintenance  of  subway  systems,  with  a  view  to 
safeguarding  workmen. 

In  some  cases  these  laws  fix  the  size  of  manholes  so  as  to  pro- 
vide sufficient  working  space  for  the  necessary  jointing  and 
repairs,  and  the  size  and  location  of  manhole  covers.  The 
proposed  National  Electrical  Safety  Code,  in  the  preliminary 
edition  issued  by  the  Bureau  of  Standards,  April  29,  1915,  con- 
tains the  following  recommendations  covering  manholes,  hand- 
holes  and  ducts: 

LOCATION 

Underground  systems  of  electrical  conductors  should  be  so  located  as  to 
be  subject  to  the  least  practicable  amount  of  disturbance.  When  being 
designed  and  installed,  care  should  be  exercised  to  avoid  catchment  basins, 
street  railway  tracks,  gas  pipes,  or  other  underground  structures  which 
have  been  installed  or  are  planned  for  the  future. 

To  facilitate  installing  and  withdrawing  cables  and  conductors,  the 
ducts  between  adjacent  manholes  or  other  outlets  should  be  installed  in 
straight  lines,  except  when  it  is  necessary  to  install  curves,  in  which  case 


28       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

they  should  be  of  not  less  than  25  ft.  radius,  and  manholes  or  other  outlets 
spaced  closer  together  than  on  straight  runs. 

GRADING 

Manholes  should  be  so  located  and  ducts  so  graded  that  drainage  of 
ducts  will  always  be  toward  manholes  or  handholes.  To  insure  satisfactory 
drainage,  the  ducts  should  be  so  installed  as  to  provide  a  grade  of  not  less 
than  3  in.  in  100  ft.  of  length. 

ACCESSIBILITY 

Manholes  should  be  so  located  as  to  provide  safe  and  ready  access,  and, 
if  possible,  so  that  the  least  horizontal  distance  from  any  rail  of  a  railroad 
track  to  the  nearest  edge  of  a  manhole  opening  is  not  less  than  3  ft. 

MECHANICAL  DETAILS 

The  mechanical  design  and  construction  of  manholes  and  handholes  shall 
be  such  as  to  provide  sufficient  strength  to  safely  sustain  the  mechanical 
loads  which  will  be  imposed  upon  them. 

The  entrance  to  all  manholes  shall  be  not  less  than  24  in.  minimum 
diameter.  Round  openings  are  recommended. 

Manholes  should  be  so  constructed  when  practicable  that  the  least 
inside  dimension  will  be  not  less  than  3  ft.  6  in.,  and  should  be  so  arranged 
as  to  maintain  a  clear  working  space  whose  least  dimensions  are  not  less 
than  3  ft.  horizontally  and  6  ft.  vertically,  except  that  where  the  opening  is 
within  1  ft.  on  each  side  of  the  full  size  of  the  manhole  the  depth  may  be  less. 
Where  conditions  will  permit,  a  larger  working  space  than  the  above  should 
be  provided. 

Manholes  and  handholes  shall  be  so  arranged,  if  practicable,  as  to  provide 
permanent  drainage  through  trapped  sewer  connections  or  otherwise  for 
such  surface  or  drainage  water  as  may  flow  into  them. 

MANHOLE  COVERS 

Manholes  and  handholes  while  not  being  worked  in  shall  be  securely 
closed  by  covers  of  sufficient  strength  to  sustain  such  mechanical  loads  as 
will  be  imposed  upon  them,  and  so  secured  in  place  that  a  tool  or  appliance 
is  required  for  their  opening  or  removal. 

MECHANICAL  BARRIERS  AND  GUARDS 

Manhole  openings  shall  be  so  arranged  that  they  may,  when  uncovered, 
be  surrounded  by  substantial  metal  barrier  guards. 

MATERIAL,  SIZE,  AND  FINISH  OF  DUCTS 

Ducts  used  in  underground  systems  of  distribution  for  electrical  supply 
and  signal  conductors  shall  be  of  such  material,  size,  mechanical  strength, 
and  finish  as  to  permit  the  safe  installation  and  maintenance  of  all  con- 
ductors or  cables  to  be  maintained  in  them. 


PRELIMINARY  SURVEY  29 


INSTALLATION  OF  DUCTS 

Conduits  should,  where  necessary,  be  laid  on  suitable  foundations  of 
sufficient  mechanical  strength  to  protect  them  from  settling  and  be  pro- 
tected by  covers  where  necessary  to  prevent  their  disturbance  by  workmen 
when  digging,  or  by  other  causes.  A  sufficient  depth  shall  be  provided 
between  the  top  of  the  duct  covering  and  pavement  surface  or  other  surfaces 
under  which  the  duct  run  is  constructed. 

Ducts  shall  have  clear  bores  and  be  freed  from  burrs  before  laying.  They 
shall  be  laid  in  line  in  such  manner  as  to  prevent  shoulders  at  joints. 

Duct  openings  into  manholes,  handholes,  or  other  permanent  openings 
of  underground  systems  shall  be  provided  with  an  effective  bushing. 

Duct  runs  should  provide  as  great  a  clearance  from  other  underground 
structures  as  practicable.  Conduits  for  underground  conduit  systems  to  be 
occupied  by  signal  conductors  for  public  use  should,  where  practicable, 
be  separated  from  underground  conduit  systems  for  supply  conductors  by 
not  less  than  3  in.  of  concrete  or  its  equivalent. 

Joints  in  duct  runs  shall  be  made  reasonably  water-tight  and  mechanically 
secure  to  maintain  individual  ducts  in  alignment. 

No  duct  should  enter  any  manhole,  handhole,  or  other  permanent  open- 
ing of  underground  systems  of  distribution  at  a  distance  of  less  than  6  in. 
above  the  floor  line  or  below  the  roof  line. 

Ducts  of  laterals  supplying  service  to  buildings  should  be  effectively 
plugged  or  cemented  by  the  use  of  asphaltum,  pitch,  or  other  suitable  means 
to  prevent  gas  entering  the  consumers'  premises  through  the  ducts. 

The  foregoing  notes  are  included  with  the  idea  that  they  may 
be  useful  to  companies  in  their  dealings  with  commissions  and 
municipal  bodies. 


CHAPTER  III 
CONDUIT  AND  MANHOLE  CONSTRUCTION 

Selection  of  Materials. — "Whether  it  is  the  intention  of  the 
central-station  engineer  to  build  the  conduit  line  himself,  or  to 
have  it  built  by  contract,  there  will  be  certain  material  and  labor 
used,  and  these  should  be  the  best  of  their  kind  in  either  case."1 
Having  decided  on  the  routes  of  the  conduit,  the  type  of  conduit 
line  to  be  constructed  should  be  determined. 

A  few  years  ago  a  3-in.  diameter  duct  was  considered  suffi- 
ciently large,  but  for  feeder  cables  called  for  today,  which  are 
often  over  3  in.  in  diameter,  nothing  less  than  a  3J^-in.  bore 
conduit  should  be  used. 

If  the  material  selected  is  of  the  best,  and  the  workmanship 
all  that  it  should  be,  there  is  no  reason  why  a  first-class  conduit 
should  not  last  indefinitely  and  the  repair  and  maintenance 
charges  be  low. 

Installation  of  Conduit. — In  the  laying  of  conduit,  trenches 
should  be  dug  to  a  line  stretched  along  the  street  to  keep  the 
ditch  straight,  and  the  width  should  be  kept  constant  by  means 
of  a  stick  cut  to  the  required  length  and  used  as  a  gage.  The 
ditch  should  be  dug  in  the  rough,  somewhat  narrower  than  the 
finished  width,  the  exact  width  being  obtained  by  trimming. 
This  method  produces  a  straight  smooth  finish  on  the  sides  of  the 
trench  and  will  aid  materially  in  keeping  the  ducts  straight  and 
also  in  reducing  the  quantity  of  concrete  required  for  any  given 
duct  section. 

The  bottom  of  the  trench  should  be  carefully  leveled  and 
graded  to  the  required  depth  and  grade  stakes  should  be  driven 
at  intervals  throughout  the  length  of  the  ditch  for  the  purpose  of 
limiting  the  thickness  of  the  concrete  base  and  of  fixing  the  exact 
grade  of  the  finished  conduit. 

Ducts  should  be  so  laid  as  to  drain  toward  manholes,  for  if 
pockets  are  formed  and  the  duct  line  is  submerged  it  is  likely 
to  freeze  in  winter  weather  and  injure  the  insulation  of  the  cable, 
and  possibly,  damage  the  conduit. 

1  HANCOCK,  N.  E.  L.  A.,  1904. 

30 


CONDUIT  AND  MANHOLE  CONSTRUCTION  31 

In  the  laying  of  conduit  great  care  should  be  taken  to  insure 
that  the  alignment  of  the  ducts  is  not  disturbed  previous  to  or 
during  the  process  of  filling  in  the  space  between  the  ducts  and 
sides  of  the  trench,  or  in  placing  the  top  cover  on  the  concrete. 

In  digging  the  trench,  paving  materials  or  old  concrete  should 
be  carefully  separated  from  the  earth  and  all  excavated  material 
should  be  thrown  well  back  from  the  brows  of  the  ditch  to  pro- 
vide wheeling  space  for  concrete  and  other  materials,  in  order  to 
prevent  them  from  being  brushed  into  the  ditch  by  workmen. 
Where  deep  ditches  are  required,  and  the  soil  is  of  an  unstable 
character,  shoring  or  bracing  will  be  necessary.  This  is  especially 
necessary  in  case  of  severe  rains  during  the  progress  of  the  work, 
and  the  force  engaged  in  the  work  should  always  be  so  arranged 
that  the  smallest  possible  amount  of  trench  consistent  with 
economical  working,  will  be  opened  at  one  time. 

In  many  cities  there  is  a  limit  set  on  the  amount  of  street  which 
may  be  opened  at  one  time. 

Where  it  is  the  intention  of  the  engineer  to  furnish  his  own 
labor  and  material  in  the  construction  of  the  conduit  line,  it  is 
essential  that  he  provide  himself  with  a  general  foreman,  or 
general  superintendent,  who  is  thoroughly  familiar  with  the 
laying  out  of  the  work,  handling  the  men  and  attending  to  the 
details  of  city-street  construction.  It  will  be  necessary  to  place 
considerable  confidence  in  this  man  and  his  ability  should  be 
such  that  the  payroll  will  be  reduced  to  a  minimum  and  the 
amount  of  work  completed  each  day  be  consistent  with  the 
number  of  men  employed. 

The  superintendent  of  construction  should  be  familiar  with 
all  of  the  details  of  the  work,  and  see  that  his  assistant  properly 
protects  the  life  and  property  of  others  observing  the  city 
regulations  and  providing  bridges  over  openings  at  intersecting 
streets.  Proper  barriers  should  be  placed  where  required,  and 
excavations  should  be  flagged  at  all  times,  to  avoid  accidents  to 
pedestrians,  or  interference  with  traffic.  The  trench  should  be 
properly  patroled  at  night  by  a  watchman,  whose  duty  it  should 
be  to  see  that  the  lanterns  are  kept  lighted  throughout  the 
night. 

It  is  important  that  records  be  made  of  the  progress  of  each 
day's  work  and  that  measurements  be  taken  showing  the  actual 
location  of  the  work,  foreign  conduits,  pipes,  and  any  other  ob- 


32       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


structions  encountered  in  the  installation,  as  well  as  any  troubles 
experienced  during  the  construction  period. 

The  principal  object  in  keeping  itemized  records  is  to  enable  the 
engineer  to  determine  the  unit  cost  for  similar  work,  and  to  analyze 
expenditures  with  a  view  to  improving  the  method  of  working, 
as  well  as  the  class  of  labor  to  be  employed.  The  records  should 
show  the  amount  of  each  class  of  work  completed  daily  so  that 
the  many  kinds  of  work  may  be  divided  into  units  and  the  unit 
cost  obtained. 

In  all  forms  of  conduit  construction  which  require  the  formation 
of  ducts,  the  base  or  foundation  section  of  concrete  should  be 
not  less  than  3  in.  in  thickness.  The  laying  of  the  conduit  should 
be  immediately  followed  by  the  concrete  required  to  fill  in  between 
the  sides  of  the  trench  and  the  conduit  line,  in  order  to  give  sup- 
port to  the  sides  of  the  trench  and  to  insure  a  proper  joining  of  the 
concrete  in  the  base  and  side  sections. 

Concrete. — The  concrete  required  for  conduit  work  should  be 
mixed  in  a  thorough  and  careful  manner.  Where  the  streets  are 
surfaced  with  a  smooth,  clean  pavement,  and  the  municipal 
authorities  will  permit  the  use  of  the  pavements,  no  mixing  board 
will  be  required.  Where  the  work  is  being  done  on  unimproved 
streets  or  rough  pavements,  mixing  boards  should  be  provided 
if  the  concrete  is  to  be  mixed  by  hand.  Mixing  boards  made  of 
a  sheet  of  boiler  iron  will  be  found  convenient.  These  should 
be  about  8  ft.  square  and  J4  m-  thick,  and  provided  with  holes 
and  rings  at  the  corners  to  which  a  length  of  chain  can  be  fastened 
to  facilitate  moving  from  place  to  place. 

TABLE  I. — MATERIALS  REQUIRED  FOR  A  CUBIC  YARD  OP  RAMMED  CONCRETE 


Mixtures 

Stone  1  in.  and 
under,  dust 
screened  out 

Stone  2^  in.  and 
under,  dust 
screened  out 

Stone  2J4  in.  with 
most  small  stone 
screened  out 

Gravel  H  in. 
and  under 

3 

•g 

t 

| 

t 

t 

i 

T3 

t 

2 

t 

i 

1 

«r 

g 

o 

i 

3 

2 

. 
•*» 

V 

3 

e 

XI 

i 

s 

1 

"S 

1 

1 

s 

1 

1 

| 

i 

1 

1 

1 

1 

i 

1 

0 

CQ 

DQ 

u 

OQ 

o 

CQ 

03           U 

OQ 

OQ 

0 

I 

QQ 

1 

2.0 

4.0 

1.46 

0.44 

0.89 

1.48    0.45 

0.90 

1.53 

0.47 

0.93 

1.34 

0.41    0.81 

1 

2.5 

5.0 

1.19 

0.461  0.91 

1.21 

0.46 

0.92J   1.26 

0.48 

0.96 

1.10 

0.42    0.83 

1 

3.0 

5.0 

1.11 

0.51 

0.851   1.14 

0.52 

0.87 

1.17 

0.54 

0.89 

1.03 

0.47J  °-78 

1 

3.0 

6.0 

1.01 

0.46    0.92 

1.02 

0.47 

0.93 

1.06 

0.48 

0.97 

0.92 

0.42 

0.84 

1 

3.0 

7.0 

0.91 

0.42    0.97 

0.92 

0.421  0.98 

0.94 

0.42 

1.05 

0.84 

0.38 

0.89 

1 

4.0 

7.0 

0.83 

0.51    0.89 

0.84 

0.51 

0.90 

0.87 

0.53 

0.93 

0.77 

0.47 

0.81 

1 

4.0 

8.0 

0.77 

0.47 

0.93 

0.78 

0.48 

0.95 

0.81 

0.49 

0.98 

0.71 

0.43 

0.86 

1 

CONDUIT  AND  MANHOLE  CONSTRUCTION  33 

Concrete  for  conduit  work  should  be  mixed  from  good  Port- 
land cement  and  clean  sand  and  gravel,  or  broken  stone,  in  the 
proportions  of  1  part  cement  to  3  parts  of  sand  and  5  parts  of 
gravel  or  broken  stone,  with  sufficient  water  to  thoroughly  wet 
the  mix,  and  allow  a  small  amount  of  water  to  come  to  the  surface 
when  the  concrete  is  ready  for  pouring. 

Most  brands  of  Portland  cement  manufactured  at  the  present 
time  appear  to  be  satisfactory  and  will  pass  the  strength  tests 
if  the  cement  is  a  representative  sample  of  the  manufacturer's 
output. 

It  is  customary  to  test  cement  for  tensile  strength,  the  reason 
being  that  concrete  is  weaker  in  tension  than  compression. 

Specifications  for  cement  may  be  obtained  from  any  of  the 
members  of  the  Association  of  Portland  Cement  Manufacturers, 
and  they  will,  therefore,  not  be  printed  here.  It  is  customary  to 
test  samples  of  cement  from  each  shipment  received,  some  engi- 
neers testing  one  sample  from  each  8  or  10  bbl.  received,  others 
testing  only  one  sample  from  each  carload.  The  number  of 
samples  to  be  tested  depends  on  the  importance  of  the  work, 
but  in  ordinary  conduit  work  and  manhole  construction  one  test 
from  each  carload  should  be  sufficient. 

There  are  several  important  considerations  to  be  observed  in 
the  selection  of  aggregates  for  concrete.  The  material  entering 
into  the  concrete  must  be  of  such  structure  and  quality  as  to  suit 
the  use  to  which  the  concrete  is  to  be  put.  Aggregates  should 
remain  in  an  unaltered  physical  state  as  long  as  the  concrete  lasts 
and  should  be  so  graded  as  to  give  a  maximum  density,  strength 
and  impermeability.  The  material  selected  should  show  a  definite 
strength  in  combination  with  the  cement. 

The  matter  of  using  a  good  quality  of  sand  is  very  important. 
All  sands  are  derived  from  the  decomposition  of  natural  rock  of 
various  kinds.  It  is  frequently  stated  in  specifications  that  clean 
sharp  sand  must  be  used,  and  while  this  is  important,  it  is  more 
important  that  sand  be  properly  graded  so  as  to  secure  a  dense 
mass.  Sand  containing  loam  or  clay  should  not  be  used,  for  if 
it  has  been  properly  washed  all  such  foreign  materials  will  have 
been  removed. 

When  mixed  by  hand,  the  cement,  sand  and  stone  should 
be  turned  at  least  three  times  dry  and  twice  wet,  and  the  concrete 
should  be  placed  immediately  after  mixing.  When  all  the  con- 
crete has  been  placed  in  the  trench,  it  should  be  allowed  to  take 

3 


34       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

its  initial  set  before  the  trench  is  filled  in  and  tamped,  and  the 
pavement  replaced  in  order  to  avoid  throwing  the  conduit  out 
of  line  or  fracturing  the  concrete  while  it  is  still  weak. 

Tile  Duct. — Tile  duct  is  made  of  clay  which  has  been  worked 
up  in  a  pug  mill  to  the  proper  consistency,  passed  through  a  press 
from  which  it  emerges  in  the  desired  shape,  carefully  dried,  and 
burned  until  it  is  thoroughly  vitrified.  It  is  then  given  a  salt 
glaze  and  allowed  to  cool  slowly. 


FIG.  15. — Single-  and  multiple-tile  duct. 

The  quality  of  the  duct  is  very  materially  affected  by  many  of 
the  processes,  and  it  is,  therefore,  important  that  it  be  purchased 
on  carefully  drawn  specifications. 

The  clay  should  be  free  from  gravel  and  of  such  composition 
that  it  will  work  up  into  a  solid  homogeneous  mass,  60  per  cent, 
fire  clay  and  34  per  cent,  shale  making  a  very  desirable  com- 
bination. 

The  duct,  when  moulded  and  dried,  should  be  burned  thor- 
oughly, but  not  scorched  or  fused.  The  glaze  should  thoroughly 
cover  the  inside -of  the  ducts  so  that  they  will  present  a  smooth 


CONDUIT  AND  MANHOLE  CONSTRUCTION  35 

surface  to  the  cable.  Single  duct  should  not  have  a  bend  of  over 
J^  in.  from  a  straight  line,  and  multiple  duct  should  not  have 
more  than  %Q  in.  bend.  Twisted  or  distorted  pieces  should  be 
rejected  as  these  cannot  be  lined  up  and  may  interfere  with  the 
installation  of  the  cable.  No  duct  having  salt  blisters  or  drips 
which  project  more  than  J^  in.  inside,  or  J4  in.  outside  should 
be  used.  Air-  and  fire-checked  pieces  should  also  be  rejected. 
The  test  for  straightness  should  be  made  by  passing  through  the 
duct  a  mandril  of  the  length  of  the  piece  and  %  in.  smaller  than 
the  inside  diameter  of  the  duct.  If  the  mandril  will  not  pass,  the 
duct  is  too  crooked  to  be  installed. 

If  the  tile  is  properly  vitrified,  it  will  give  a  clear  ringing  sound 
when  struck  by  a  piece  of  tool  steel.  If  it  gives  a  dead  sound,  it 
indicates  softness  and  porosity,  which  will  result  in  a  high  break- 
age in  handling. 

Tile  conduit  will  last  indefinitely,  and  when  free  from  iron  it 
possesses  high  insulating  properties.  It  also  has  great  mechan- 
ical strength,  and  shows  an  average  puncture  test  of  25,000  volts 
dry,  and  21,000  volts  after  immersion  in  water  for  several  days. 
While  the  dielectric  strength  of  the  tile  is  very  high,  the  insulation 
resistance  of  the  system  is  greatly  lowered  in  consequence  of  the 
number  of  joints  which  are  made  with  cement  or  other  moisture- 
absorbing  material.  Instead  of  the  entire  system  withstanding 
20,000  volts,  it  will  be  found  that,  due  to  the  presence  of  joints, 
the  installation  will  not  be  able  to  stand  more  than  5,000  volts, 
depending,  however,  on  the  general  characteristics  of  the  soil 
surrounding  the  ducts. 

Multiple-tile  conduit  is  usually  made  in  lengths  of  3  ft.,  the 
number  of  ducts  varying  from  two  to  nine,  and  in  some  special 
installations  even  more. 

The  pieces  are  laid  end  to  end  and  are  usually  held  in  align- 
ment during  the  construction  period  by  iron  dowel  pins  which  fit 
into  the  holes  formed  in  the  ends  of  each  section. 

In  making  joints  in  multiple-duct  tile,  it  is  impossible  to  pre- 
vent communication  between  the  ducts,  and,  owing  to  this  con- 
dition, multiple-duct  affords  the  least  protection  to  the  cables. 
If  the  streets  in  which  the  conduit  is  to  be  installed  are  congested 
under  the  surface,  the  use  of  single-tile  duct  permits  of  a  more 
flexible  installation,  whereas,  the  multiple-tile  duct  is  used  to 
good  advantage  in  suburban  districts  where  there  are  few  ob- 
structions to  interfere  with  the  course  of  the  line. 


36       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

Multiple-tile  duct  is  better  adapted  for  telephone,  telegraph 
and  other  similar  wires  than  for  use  in  connection  with  power 
cables,  since,  as  explained,  the  ducts  communicate  at  each 
joint  between  the  sections  of  tile,  and  in  case  of  trouble  on  a 
cable,  in  addition  to  the  communication  at  each  joint,  the  thin 
tile  is  apt  to  be  melted  and  evaporated,  permitting  the  burning 
cable  to  damage  other  cables  in  the  same  conduit  line. 

In  the  laying  of  single-duct  tile,  the  ordinary  methods  of  brick 
laying  are  used  and  the  joints  are  made  by  simply  putting  the 


a 


FIG.  16. — Section  of  tile  conduit  illustrating  use  of  mandril. 

two  pieces  of  tile  together.  Alignment  is  secured  by  the  aid  of  a 
mandril.  Since  the  length  of  the  sections  is  shorter  and  the 
area  much  less  than  in  the  case  of  multiple-tile,  a  more  perfect 
butt  joint  can  be  obtained  in  a  single-duct  installation. 

It  is  not  customary  in  laying  single-duct  tile  to  wrap  the  joint 
with  any  form  of  protection  to  prevent  the  mortar  or  concrete 
running  through  the  joint.  It  is  almost  certain,  however,  that 
some  mortar  will  work  its  way  through  the  joint  and  in  order  that 
this  may  be  removed  before  it  hardens,  a  wooden  mandril,  such 
as  is  shown  in  Fig.  16,  3  in.  in  diameter  and  about  30  in.  in  length, 
is  used.  At  one  end  is  provided  an  eye  (a),  which  maybe  engaged 
by  a  hook,  in  order  to  draw  it  through  the  conduit,  while  at 


CONDUIT  AND  MANHOLE  CONSTRUCTION 


37 


the  other  end  is  secured  a  rubber  gasket  (6)  having  a  diameter 
slightly  larger  than  that  of  the  interior  of  the  duct.  One  of  these 
mandrils  is  placed  in  each  duct  when  the  work  of  laying  is  begun. 
As  the  work  progresses,  the  mandril  is  drawn  along  through  the 
duct  by  the  workmen  by  means  of  an  iron  hook  at  the  end  of  a 


6  DUCT'S. 


/£  &UCTS. 


FIG.  17. — Single-tile  duct  sections. 

rod  about  3  ft.  long.  By  this  means  the  formation  of  shoulders 
on  the  inner  walls  of  the  ducts  at  the  joints  is  prevented,  and 
any  dirt  that  may  have  dropped  into  the  duct  is  also  removed. 
The  cylindrical  part  of  the  mandril  insures  good  alignment  of  the 
ducts,  thus  securing  a  perfect  tube  from  manhole  to  manhole. 
The  use  of  such  a  device  will  leave  a  smooth  inner  surface,  free 


38       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


from  projections  and  burrs,  which  if  left  would  be  likely  to  dam- 
age the  sheaths  of  the  cables  during  the  drawing-in  process. 

The  principal  advantage  to  be  gained  from  the  use  of  single- 
duct  lies  in  the  ability  to  break  joints  in  all  ducts.  Provided  a 
jacket  of  concrete  or  mortar  surrounds  each  individual  longitu- 
dinal row  of  tiles,  perfectly  solid  ducts  may  be  produced.  If  the 
tiles  are  not  completely  surrounded  by  such  a  jacket,  a  burning 
cable  is  very  likely  to  discharge  the  gases  produced  by  the  arc 
through  the  butt  joints  with  such  force  that  the  hot  gases  and  the 
flame  which  results  from  their  combustion  will  cause  damage  to 
the  cables  in  adjacent  ducts. 

Single-duct  tile,  being  vitrified,  requires  the  same  general 
provisions  for  inspection  as  multiple-duct  and  all  duct  purchased 
should  be  rigidly  inspected  at  the  factory  before  shipment  is 
made. 

The  weight  of  3J^-in.  tile  is  approximately  8  Ib.  per  duct  ft. 
and  this  heavy  weight  increases  the  freight  cost  and  the  labor 
cost  of  laying. 

The  question  of  breakage  is  an  item  which  must  be  taken  into 
consideration.  This  will  vary  from  5  to  10  per  cent,  of  the  total 
shipment,  depending  upon  the  composition,  quality  and  firing 
of  the  clay  of  which  the  duct  is  made. 

TABLE   II. — TABLE   OP  INFORMATION  ON  STANDARD  VITRIFIED   CONDUIT 


Style  ofjconduit 

Dimension 
of  square 
duct,  in. 

Dimension 
of  round 
duct,  in. 

Outside 
dimen- 
sions of 
end  section, 
in. 

Reg. 
stock 
lengths, 
in. 

Short 
lengths, 
in. 

Approx. 
weight 
per  duct 
ft.,  Ib. 

2-duct  multiple  
3-duct  multiple  
4-duct  multiple  
6-duct  multiple  
9-duct  multiple  

3%sq. 
3%sq. 
3Hsq. 
3X  sq. 
3Hsq. 

3M 
3H 
3H 

3tf 
3H 

5  by  9 
5  by  13 
9  by  9 
9  by  13 
13  by  13 

24 
24 
36 
36 
36 

6,  9  and  12 
6,  9  and  12 
6,  9  and  12 
6,  9  and  12 
6,  9  and  12 

8 
8 
8 
8 
8 

3% 

5  by  5 

18 

6,  9  and  12 

8 

Single  duct,  self-cen- 
tering   

3?£ 

5  by  5 

18 

6,  9  and  12 

10 

Round  single  duct, 
self-centering  



3H 

5  in. 
round 

18 

6,  9  and  12 

10 

Minimum  car  lot,  5,000  duct  ft.  or  40,000  Ib. 
Maximum  car  lot,  7,500  duct  ft.  or  60,000  Ib. 


Where  very  cheap  work  is  desired,  multiple-duct  tile  is  some- 
times laid  either  without  concrete  or  with  a  single  bottom  layer 
for  a  foundation  and  with  perhaps  a  top  layer  for  protection 


CONDUIT  AND  MANHOLE  CONSTRUCTION 


39 


against  future  excavations.  The  concrete  in  such  cases  gives 
little  or  no  support  to  the  tile  and  should  the  earth  shift  or  settle, 
the  tile  is  apt  to  give  way  under  the  strain,  resulting  in  damage 
to  the  cables.  Such  construction  is  not  recommended  and  in 
no  case  should  it  be  used  where  permanency  is  desired. 

In  the  laying  of  tile  duct  both  of  the  single  and  multiple  type 
the  ducts  should  all  be  thoroughly  cleaned  out  by  drawing  through 


^£#£&££ 


DUCT. 


/s" 


«  DUCT: 


DUCT: 


££££&£ 


/s' 


4  DUCT. 


/2  OUCT 

FIG.  18. — Multiple-tile  duct  sections. 

them  a  wire  brush  or  flue  cleaner  slightly  larger  than  the  duct. 
Any  particles  of  sand  or  loose  bits  of  mortar  left  in  the  duct  may 
be  removed  by  following  up  the  brush  or  cleaner  with  a  cotton- 
rope  mop.  It  is  essential  that  the  cleaning  be  done  as  soon  as 
possible  after  the  placing  of  the  concrete  in  order  that  concrete 
or  mortar  which  may  have  been  introduced  into  the  ducts  through 


40       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

the  joints  may  be  removed  before  it  has  a  chance  to  harden. 
Where  it  is  necessary  to  cut  pieces  of  the  tile  for  fitting  lengths 
together,  the  tile  is  notched  all  around  at  the  desired  point  by 
means  of  a  hammer  and  cold  chisel.  It  should  break  off  at  the 
mark  after  continued  chipping,  though  it  frequently  happens  that 
the  cracks  run  off  in  some  other  direction.  It  is,  preferable, 
therefore,  to  have  fitter  lengths,  furnished  by  the  manufacturer. 

Stone  Duct. — Stone  duct  has  been  used  quite  extensively  in  the 
City  of  Chicago.  It  is  made  of  a  high  grade  of  limestone  and 
Portland  cement,  in  the  proportions  of  4.75  to  1.00,  the  materials 
being  thoroughly  blended  together  with  water. 

Moulded-stone  duct  is  manufactured  under  the  Graham  process 
and  is  moulded  in  two  half  moulds  or  sections  in  especially 
designed  machines.  This  mould  contains  a  mandrel  form  that  is 
displaced  by  a  larger  mandrel  having  a  tapered  steel  point. 
Both  mandrels  are  revolved  by  means  of  individual  motors  and 
the  tables  holding  the  moulds  are  moved  parallel  with  the 
mandrels.  As  the  form  is  displaced  by  the  tapered  steel  points, 
all  inequalities  in  filling  are  eliminated. 

This  method  insures  a  perfectly  smooth  inner  and  outer  sur- 
face of  the  pipes.  After  being  removed  from  the  conduit 
machines,  the  ducts  are  allowed  to  stay  in  the  lower  half  of 
the  mould  for  48  hr.  to  take  their  initial  set.  They  are  then 
placed  in  racks  and  sprinkled  continuously  for  about  6  weeks  to 
insure  their  perfect  curing,  after  which  they  are  allowed  to  dry 
for  2  weeks.  They  are  then  ready  for  use.  The  ducts  are  made 
in  5-ft.  lengths  and  the  units  are  provided  with  metal  rings. 
These  rings,  which  are  used  for  connecting  two  sections  together 
afford  a  tight  joint,  making  it  impossible  for  any  foreign  material 
to  get  into  the  duct.  It  is  claimed  that  this  type  of  conduit  is 
not  injured  even  by  the  short-circuiting  of  heavy  power  cables. 
In  this  way  communication  of  trouble  from  one  duct  to  another 
is  avoided. 

This  conduit  is  laid  with  an  envelope  of  concrete.  It  forms  a 
monolithic  mass  as  the  envelope  makes  an  excellent  bond  with 
the  duct.  The  ducts  can  be  readily  cut  with  an  ordinary  cross- 
cut saw,  and  the  weight  of  the  duct  is  approximately  the  same 
as  that  of  tile  duct.  With  the  use  of  metal  sleeves,  unskilled 
labor  may  be  employed  in  its  installation.  Its  length  permits  of 
the  same  staggering  as  is  obtained  with  the  use  of  fiber  conduit. 
The  conduit  is  made  up  in  various  forms  and  in  split  sections, 


CONDUIT  AND  MANHOLE  CONSTRUCTION  41 

thus  allowing  repairs  to  be  made  in  ducts  carrying  cables.  It 
weighs  approximately  7J£  Ib.  per  ft.,  has  a  bore  of  3^  in.,  with 
a  wall  %  in.  thick  and  approximately  4,000  ft.  can  be  loaded  for 
shipment  on  a  standard  car. 

Fiber  Duct. — Fiber  conduit  is  the  most  recent  addition  to  the 
materials  used  for  subway  construction,  and  has  come  into  very 
general  use  for  all  classes  of  underground  electrical  work.  This 
type  of  conduit  has  been  in  use  approximately  15  years,  and  the 
writer  has  had  occasion  to  examine  fiber  duct  which  has  been 


FIG.  19. — Stone  conduit. 

installed  in  moist  soil  for  about  10  years.  The  inspection  failed 
to  show  the  slightest  signs  of  deterioration.  Fiber  pipe  was 
originally  used  for  irrigation  purposes  and  was  installed  under  the 
most  unfavorable  conditions  in  all  kinds  of  soil,  both  wet  and 
dry,  and  in  a  number  of  cases  without  any  concrete  or  cement 
protection.  It  is  made  of  wood  pulp  which  has  been  thoroughly 
saturated  with  a  bituminous  compound  containing  about  6 
per  cent,  of  creosote  in  solution.  The  creosote  prevents  rotting 
by  killing  the  organisms  which  might  act  on  the  vegetable 
matter  in  the  pulp.  The  conduit  is  made  in  various  styles  of 


42       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


joint  to  suit  the  particular  service  conditions;  sleeve,  drive  or 
screw  joints  may  be  obtained  as  required.  The  joints,  which  are 
turned  up  true  in  a  lathe  during  the  process  of  manufacture, 
are  self-aligning. 

TABLE  III. — DATA  ON  FIBER  CONDUIT 


Inside  diameter, 
in. 

Type  of  conduit 

Approximate 
average  weight 
per  ft.-lb. 

Feet  in  mini- 
mum car  ship- 
ped in  bulk 

Average  load 
one-team 
truck,  ft. 

1 

Socket  joint 

0.38 

80,000 

10,500 

m 

Socket  joint 

0.70 

42,000 

5,700 

2| 

Socket  joint 

0.85 

35,000 

4,700 

2H 

Socket  joint 

1.02 

30,000 

4,000 

3 

Socket  joint 

1.20 

25,000 

3,300 

m 

Socket  joint 

1.45 

21,000 

2,750 

4 

Socket  joint 

1.62 

18,000 

2,450 

IK 

Sleeve  joint 

0.74 

40,000 

5,400 

2 

Sleeve  joint 

0.90 

33,000 

4,400 

2H 

Sleeve  joint 

1.10, 

27,000 

3,600 

3 

Sleeve  joint 

1.30 

23,000 

3,000 

5H 

Sleeve  joint 

2.50 

12,000 

1,600 

4 

Sleeve  joint 

3.20 

9,400 

1,250 

2 

Harrington  joint 

0.90 

33,000 

4,400 

2H 

Harrington  joint 

1.10 

27,000 

3,600 

3 

Harrington  joint 

1.30 

23,000 

3,000 

8H 

Harrington  joint 

1.55 

19,300 

2,550 

4 

Harrington  joint 

1.90 

15,500 

2,100 

3 

Screw  joint 

2.20 

13,600 

1,800 

3H 

Screw  joint 

2.50 

12,000 

1,600 

4 

Screw  joint 

3.20 

9,400 

1,250 

2 

"Linaduct" 

0.55 

54,000 

7,300 

2^ 

"Linaduct" 

0.65 

42,000 

6,100 

3 

"Linaduct" 

0.75 

24,000 

5,300 

3^ 

"Linaduct" 

0.85 

21,500 

4,700 

These  joints  make  it  possible  to  lay  the  sections  in  the  trench 
unit  by  unit  with  great  rapidity.  No  wrapping  with  burlap 
or  other  material  is  required  and  no  trowel  work  is  necessary, 
thus  permitting  employment  of  unskilled  labor  in  laying  the 
duct. 

Where  it  is  desirable  to  make  a  perfectly  water-tight  joint, 
liquid  compound  is  usually  applied  to  the  male  end  of  each  section 
as  it  is  placed  in  position.  The  simplicity  of  this  form  of  duct 
and  the  ease  of  handling  give  it  an  important  advantage  over 
other  classes  of  duct.  When  the  ends  are  properly  fitted  together, 
they  remain  in  perfect  alignment. 


CONDUIT  AND  MANHOLE  CONSTRUCTION  43 

Tests  which  have  been  conducted  on  fiber,  show  that  it  will 
withstand  a  puncture  test  of  32,000  volts  when  dry  and  24,000 
volts  after  immersion  in  water  for  about  200  hr.  It  is  impervious 
to  moisture,  gases,  acids  and  other  corrosive  elements  and  as  it 
is  a  non-conductor,  troubles  from  stray  currents  are  negligible. 

The  non-abrasive  feature  of  the  conduit  is  very  important, 
as  it  permits  of  drawing  cables  into  the  ducts  without  injury  to 
the  sheaths  by  such  grinding  or  cutting  action  as  often  results 


FIG.  20. — Installation  of  fiber  and  multiple  duct. 

when  the  ducts  are  composed  of  a  hard  material  and  the  inner 
wall  is  not  perfectly  smooth. 

Absence  of  abrasive  or  gritty  surfaces  adds  to  the  ease  and 
rapidity  with  which  the  cable  may  be  installed.  The  lightness 
of  the  conduit  gives  it  a  decided  advantage  not  only  as  regards 
handling  and  laying,  but  also  as  regards  shipping,  since  about 
20,000  ft.  can  be  loaded  in  a  standard  box-car,  owing  to  the  light- 
ness of  the  conduit.  It  is  made  in  5-ft.  lengths,  which  is  a  con- 
venient length  for  shipping  and  handling  in  the  trenches;  this 
also  results  in  fewer  joints,  thereby  effecting  a  considerable 
saving  in  labor. 


44       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


Bearing  in  mind  its  light  weight,  the  lengths  of  the  sections 
in  which  it  is  manufactured,  and  the  simplicity  in  the  method  of 
jointing,  it  is  readily  seen  that  a  greater  amount  can  be  laid  in 
less  time  by  a  less  number  of  men  than  is  the  case  with  other  forms 
of  duct.  Unskilled  labor  can  be  used  in  its  installation  and  the 


20  DUCTS. 


<7  &UCTS. 


&  DUCTS. 


/G>  DUCTS. 


S3" 


WSSSKSS* 

:•.'*>.•  ^  ?.-•?•.•.•  •  •."..> 


4-  DUCTS. 


/a 


FIG.  21.  —  Fiber-duct  sections. 


cost  of  laying  is  thereby  considerably  reduced.  Breakage 
amounts  to  practically  nothing  owing  to  the  great  tensile  strength 
and  the  shock-resisting  properties  of  the  material. 

In  the  laying  of  fiber  conduit  a  concrete  base  3  in.  thick  is 
provided  similar  to  that  used  in  other  forms  of  construction. 
There  is  also  provided  a  side  and  top  cover  with  1  in.  of  concrete 
separating  the  adjacent  duct,  and  with  fiber  conduit,  as  well  as 
with  other  forms,  it  is  well  to  avoid  water  pockets  in  the  ducts. 


CONDUIT  AND  MANHOLE  CONSTRUCTION 


45 


After  the  foundation  of  concrete  has  been  placed,  the  first  or 
bottom  row  of  pipes  is  laid  directly  on  its  surface  and  these  are 
spaced  by  means  of  a  wooden  spacing  block  or  comb,  illustrated 
in  Fig.  22.  The  desired  duct  section  is  then  built  up  in  succes- 
sive tiers  and  a  1-in.  spacing  is  maintained  throughout  the  line 
of  conduit  by  means  of  the  spacing  block  just  mentioned.  In 
laying  the  duct  care  should  be  taken  to  stagger  the  joints  in  the 
adjacent  pipes  in  the  conduit,  and  it  is  important  that  all  joints 
be  perfectly  tight,  otherwise  the  concrete  is  apt  to  work  into 
the  duct  and  cause  obstructions. 

The  concrete  should  be  worked  thoroughly  around  each  pipe 
to  prevent  voids  in  the  structure,  and  for  this  kind  of  work  the 
concrete  should  be  mixed  with  gravel  or  broken  stone,  which  will 


m 


"HT 


W 


A. 


A. 


(A)  THtS  D/MEMS 


FIG.  22.  —  Detail  of  comb  for  spacing  fiber  ducts. 

pass  through  a  sieve  of  %-in.  mesh.  In  laying  the  fiber  duct, 
each  piece  should  be  inspected  to  see  that  it  is  perfect  and  that  no 
foreign  material  has  lodged  inside  the  tube. 

In  considering  the  merits  of  the  numerous  kinds  of  conduit 
material,  which  are  used  in  underground  systems,  it  must  be 
understood  that  each  has  its  particular  field  and  the  conditions 
which  will  govern  the  type  of  installations  are  to  be  carefully 
considered,  not  only  from  the  standpoint  of  interest  and  depre- 
ciation on  the  investment,  but  also  with  a  view  to  securing  free- 
dom from  interruptions  to  service. 

The  question  of  the  relative  mechanical  strength  of  fiber,  tile 
and  stone  conduit  is  of  minor  importance,  because  the  strength 
of  the  surrounding  concrete  will  determine  the  strength  of  the 
structure  as  a  whole.  Since  the  best  grade  of  concrete  will 
stand  a  compression  test  of  about  3,000  Ib.  per  sq.  in.,  it  will  be 
seen  that,  regardless  of  the  duct  material,  the  structure  will 


46       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

have  sufficient  strength  to  meet  the  most  exacting  demands  of 
service  conditions. 

Manhole  Construction. — Manholes  are  usually  built  at  street 
intersections  or  turns  in  the  conduit  line,  to  afford  a  place  for 
jointing  the  cables.  The  distance  between  these  manholes 
depends  on  local  conditions.  It  is  safe  to  say  that  this  limiting 
distance,  where  large  cables  are  to  be  employed,  should  be 
500  ft. 

In  pulling  in  long  runs  of  cable,  the  sheath  is  subjected  to 
severe  strains  which  are  to  be  limited  as  much  as  possible. 

Manholes  designed  for  high-tension  cables  should  be  spacious 
and  should  have  good  drainage  facilities.  Their  design  should 
be  such  as  to  avoid  sharp  bends  between  the  point  where  the 
cables  enter  and  the  position  on  the  manhole  wall  where  they  are 
to  be  jointed  and  racked. 

Ample  facilities  should  be  provided  in  each  manhole  for  the 
shelves  or  racks  on  which  the  cables  are  to  be  supported.  Many 
cables  have  had  to  be  renewed  on  account  of  insufficient  manhole 
room  and  careless  racking. 

It  is  also  wise  to  give  some  attention  to  the  location  of  the  lower 
and  top  ducts  in  the  manholes  to  permit  drawing  in  cables 
without  damaging  them. 

Manhole  covers  are  preferably  located  at  the  center  of  the 
manhole  making  it  easy  to  set  and  rack  cables  and  rendering  it 
impossible  for  careless  workmen  to  ruin  the  cables  by  using  them 
as  steps  in  entering  and  leaving  manholes. 

In  transmission  systems  it  is  very  desirable,  as  previously 
stated,  to  limit  the  distance  between  manholes  to  less  than  500 
ft.,  as  this  permits  of  carrying  in  stock  standard  lengths  of  cable 
which  can  be  used  in  any  part  of  the  transmission  line.  Wher- 
ever practicable  manholes  should  be  connected  to  sewers  so 
that  the  water  will  run  off.  A  suitable  trap  should  be  employed 
to  prevent  the  sewer  water  from  backing  up  and  filling  the  man- 
hole or  conduit  line.  Where  it  is  impossible  to  make  the  neces- 
sary connection  to  the  sewer,  the  following  method  may  be  used 
to  advantage: 

When  excavating  for  manhole  work,  a  hole  a  trifle  deeper 
and  larger  than  an  ordinary  barrel  is  dug  and  a  barrel  without 
top  or  bottom  placed  in  it;  the  outside  of  the  barrel  is  surrounded 
with  a  concrete  covering  about  3  in.  thick  and  the  barrel  filled 
with  gravel  or  small  stones.  The  concrete  foundation  of  the 


CONDUIT  AND  MANHOLE  CONSTRUCTION  47 

manhole  should  then  be  laid  and  the  top  of  the  barrel  set  flush 
with  the  floor. 

The  tendency  in  the  past  has  been  to  give  too  little  attention 
to  the  matter  of  future  requirements  and  this  has  resulted  in 
the  very  congested  condition  of  cables  and  equipment  now  found 
in  the  manholes  of  many  of  our  large  cities.  The  importance  of 
providing  adequate  facilities  will  be  appreciated  when  it  is  con- 
sidered that  the  efficiency  of  men,  when  working  under  cramped 
conditions,  is  seriously  impaired. 

Sewer  and  Illuminating  Gas. — In  the  construction  of  manholes, 
provisions  should  be  made  for  sufficient  ventilation  to  carry  off 
any  gases  which  may  accumulate. 

The  gases  most  commonly  found  in  manholes  are  sewer  gas 
and  illuminating  gas,  and  now,  with  the  extensive  use  of  automo- 
biles, we  may  find  gasolene  vapors  mixed  with  the  sewer  gas. 

Sewer  gas  consists  of  approximately  90  parts  of  nitrogen, 
2  to  4  parts  of  oxygen,  1  to  3  parts  of  carbon  dioxide,  3  to  5 
parts  of  carbon  monoxide,  methane  and  other  gases.  It  has  an 
odor  due  to  the  organic  decomposition  constantly  going  on  in  the 
sewers.  It  is  not  poisonous  in  the  true  sense  of  the  word,  but, 
due  to  its  high  percentage  of  nitrogen  and  its  low  percentage  of 
oxygen,  there  is  not  a  sufficient  amount  of  oxygen  to  support 
respiration,  and  hence  a  person  is  slowly  smothered  in  an 
atmosphere  of  this  gas.  It  is  non-explosive  in  itself,  and,  due  to 
its  high  nitrogen  and  low  oxygen  content,  would,  undoubtedly, 
prevent  the  explosion  of  otherwise  explosive  gas  when  mixed  with 
it.  This  gas  easily  finds  its  way  into  the  conduit  lines  through  the 
entrapped  connections  which  the  manholes  have  with  the  sewers. 

Illuminating  gas,  or  city  gas,  as  generally  distributed,  may  be 
coal  gas,  water  gas,  Solvay  gas,  or  a  mixture  of  any  two  or  all  of 
these  gases.  It  is  colorless,  but  usually  has  a  strong  penetrating 
odor,  so  that  a  small  percentage  may  readily  be  detected  by  the 
sense  of  smell.  It  is  very  poisonous  in  itself  and  with  air  forms 
a  highly  explosive  mixture.  Gas  mains  and  distribution  lines  are 
closely  interwoven  with  the  conduit  lines  and  breaks  or  leaks  in 
the  gas  system  lead  to  the  escape  of  the  gas  into  the  conduits  and 
manholes. 

Sealing  of  Ducts  in  Manholes. — When  troubles  occur  in  which 
there  is  an  arc  in  series  with  considerable  resistance,  the  lack  of 
sufficient  oxygen  for  the  combustion  of  the  gases,  which  are  gener- 
ated, will  cause  these  gases  to  flow  through  the  conduits  and  burn 


48       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION      - 

in  adjacent  manholes,  unless  there  is  some  positive  barrier  to 
prevent  the  gas  flowing  between  manholes.  It  is,  therefore, 
considered  advisable  to  cement  the  ducts  in  each  manhole  along 
the  heavier  runs  of  cable  where  the  spreading  gas  could  cause 
the  greatest  damage.  Some  companies  using  concentric  cables, 
subject  to  creeping  on  account  of  expansion  and  contraction 
at  periods  of  heavy  and  light  loads,  do  not  consider  it  advisable 
to  cement  the  ducts.  They  also  consider  the  omission  of  the 
sealing  of  the  ducts  an  advantage  from  the  standpoint  of  provid- 
ing more  ventilation  to  the  manholes  and,  therefore,  less  chance 
of  accumulation  of  gases,  and  perhaps  increased  heat  radiation 
in  the  ducts.  All  ducts  or  pipes  leading  from  manholes  to  the 
premises  of  customers  should  be  cemented  in  the  subway  and 
at  the  entrance  into  the  customer's  buildings  to  prevent  obnoxious 
gases  entering  the  premises.  Several  devices  are  on  the  market 
which  have  been  designed  to  be  placed  in  the  duct  before  apply- 
ing a  mortar  to  aid  in  removing  the  latter.  A  weak  cement 
mortar  is  sufficient  for  this  purpose. 

Types  of  Manhole  Construction. — Manhole  construction  may 
be  classified  under  three  headings : 

(a)  Brick  construction. 

(6)  Monolithic  concrete  construction. 

(c)  Concrete  block  construction. 

The  design  of  each  of  these  three  types  of  construction  may  be 
divided  into  two  classes:  namely,  design  to  properly  facilitate 
the  training  of  cables  for  transmission  purposes;  and  design  to 
provide  for  the  training  of  cables  for  distribution  purposes,  in- 
cluding the  installation  of  transformers,  boxes,  and  other  sub- 
surface equipment. 

Monolithic  concrete  seems  to  be  advocated  for  manhole  con- 
struction, particularly  where  a  number  of  manholes  of  the  same 
size  are  to  be  built,  and  where  local  conditions  and  the  space 
available  in  the  street  will  permit  the  use  of  a  standard  form. 
One  of  the  advantages  of  the  use  of  monolithic  concrete  for  man- 
hole construction  is  the  fact  that  common  labor  may  be  employed 
for  mixing  and  placing  the  concrete,  whereas,  with  brick  construc- 
tion, the  service  of  experienced  masons  is  necessary.  Brick 
construction  seems  to  be  very  desirable  in  congested  sections 
where  the  use  of  either  a  wooden  or  metal  form  for  concrete  work 
would  be  almost  prohibitive  on  account  of  the  high  cost  of  special 
forms  to  meet  the  local  conditions. 


CONDUIT  AND  MANHOLE  CONSTRUCTION  49 

One  of  the  disadvantages  in  the  use  of  concrete  manholes  lies 
in  the  fact  that  the  soil  in  many  locations  is  sandy  clay,  which 
will  not  stand  unless  properly  supported  by  bracing.  The  result 
of  this  soil  condition  is  that  in  the  locations  where  the  absence 
of  other  constructions  permits  the  use  of  concrete  manholes,  the 
soil  requires  an  outer  as  well  as  an  inner  form.  In  such  cases  the 
resulting  cost  is  higher  than  for  brick  manholes.  The  presence 
of  water  in  some  localities  at  a  depth  of  3  or  4  ft.  makes  it  neces- 
sary to  build  brick  manholes.  In  such  locations,  a  manhole  of 
brick  can  be  built  by  driving  sheet  piling  and  using  a  sufficient 
number  of  pumps'  to  remove  the  water  from  the  hole.  The  brick- 
work is  started  directly  upon  the  sand  and  the  manhole  is  rilled 
up  with  sand  as  the  work  progresses.  This  prevents  the  water 
which  seeps  into  the  hole  washing  out  the  mortar  of  the 
brickwork. 

Building  Manholes  in  Quicksand. — It  is  frequently  necessary 
to  build  manholes  in  a  sandy  soil  when  the  permanent  water  level 
is  only  2  or  3  ft.  below  the  surface,  and  in  such  cases  manholes 
have  been  successfully  built  by  using  a  modified  form  of  open- 
caisson  construction.  The  excavation  to  the  quicksand  is  made 
in  the  ordinary  manner.  Then  a  wooden  framework  is  built, 
having  the  same  horizontal  section  as  the  manhole  wall.  This 
framework  is  built  up  of  2-in.  planks  to  a  total  thickness  of  6  in., 
the  corners  being  well  fastened  to  eliminate  diagonal  bracing  and 
leave  the  center  of  the  framework  free  for  the  excavation.  The 
framework  is  then  placed  in  a  level  position  on  the  quicksand  and 
the  manhole  is  built  of  brick  to  the  required  height,  the  walls 
being  well  plastered  on  the  outside. 

After  setting  for  3  or  4  days,  the  excavation  of  the  manhole 
proceeds.  By  digging  along  the  walls  inside  of  the  manhole  and 
under  the  wooden  framework,  the  manhole  will  usually  settle 
to  the  required  depth.  During  the  excavation  only  sufficient 
water  should  be  removed  to  allow  the  men  to  work  to  advantage, 
as  otherwise  the  sand  becomes  quite  hard.  The  settlement,  if 
slow,  can  be  accelerated  by  placing  bags  of  sand  or  other  weights 
on  top  of  the  manhole  walls.  Ordinarily  the  excavation  and 
settlement  of  the  manholes  to  the  required  depth  will  not  require 
more  than  8  or  10  hr.  unless  obstructions  are  encountered.  After 
the  manhole  has  reached  the  proper  depth,  the  settlement  is 
stopped  by  backfilling  the  excavation  and  tamping  around  the 
outside  of  the  manhole  wall. 


50       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

Upon  completion  of  the  settlement,  the  water  is  removed  from 
the  manhole,  the  sand  excavated  to  the  level  of  the  bottom  of  the 
wooden  framework  and  a  heavy  concrete  bottom  is  placed  in  the 
manhole.  The  openings  for  the  conduit  are  cut  in  the  manhole 
walls  after  it  is  entirely  completed  and  has  settled  to  the  proper 
depth. 

In  building  such  manholes,  the  labor  cost  is  about  double  that 
of  the  ordinary  manholes.  The  wooden  framework  is  the  only 
other  additional  item  of  expense. 

Concrete  blocks  have  not  been  used  to  any  considerable  extent 
for  building  manholes,  although  this  form  of  construction  would, 
undoubtedly,  be  the  cheapest  if  a  considerable  number  of  man- 
holes of  a  standard  size  were  to  be  built.  One  reason  why  this 
type  of  construction  is  not  more  common  is  the  difficulty  of 
making  connections  between  the  manhole  and  the  conduit  lines. 
Concrete  manholes  are  limited  to  localities  in  which  the  under- 
ground conditions  permit  the  use  of  standard  sizes  and  shapes, 
and  where  the  ground  is  of  sufficiently  firm  composition  as  to 
require  no  outer  form  for  the  concrete.  Moreover,  concrete 
manholes  should  be  allowed  at  least  48  hr.  for  setting,  which 
practically  prevents  their  use  in  streets  with  dense  traffic.  The 
brick  manhole  is  preferable  where  irregular  shapes  only  can  be 
used  and  where  a  large  number  of  future  connections  are  to  be 
made,  it  being  much  less  liable  to  damage  by  these  connections 
than  the  concrete  manholes. 

Roof  Construction. — Manhole  roofs  are  sometimes  built  of 
second-hand  T-rails  laid  in  two  layers  crosswise  and  filled  in 
with  concrete.  I-beams  and  other  standard  shapes  are  also 
used,  and  sometimes,  on  moderate  spans,  concrete  reinforced 
with  expanded  metal.  The  iron  roof  framing  should  be 
thoroughly  embedded  in  the  concrete  for  protection  and  to 
avoid  corrosion. 

While  cables  and  other  manhole  equipment  are  usually  so 
constructed  as  to  operate  successfully  when  submerged  in  water, 
it  is  desirable  to  have  manholes  free  of  water.  It  is  the  general 
practice  to  install  sewer  connections,  which  are  usually  provided 
with  a  back-trap  valve.  Drains  are  particularly  necessary  for 
those  manholes  which  contain  transformers  and  other  equipment 
that  should  not  be  flooded. 

Type  of  Cover. — There  are  several  types  of  manhole  heads  in 
use,  both  round  and  rectangular,  the  round  type  being  more 


CONDUIT  AND  MANHOLE  CONSTRUCTION 


51 


3>f 


PL.  AM  AN**  SfCT/ON. 


'^MerAi.  TO  *£  KNOCKED 
OUT  Off  LEFT  IN  AS 


&£TA/t.5  Or/^/VAME 

Coves?. 


FIG.  23. — Small  round  manhole  head  and  cover. 


37*' 


COUNTERSUNK  ~\  xx-  ft.  METAL.  TO  ae  KNOCKED 


AMD 


FIG.  24. — Large  "round  manhole  head  and  cover. 


52       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


generally  used.  The  use  of  rectangular  covers  should  be  avoided 
as  far  as  possible,  as  in  the  hands  of  careless  workmen  the  cover 
may  be  dropped  into  the  manhole  causing  damage  to  cables  and 
equipment.  Some  companies  use  an  inner  cover,  which  is 
fastened  tightly  to  the  outer  frame  by  means  of  a  lock  bar  and  nut 
and  made  waterproof  by  a  rubber  gasket.  In  some  installations 
this  inner  cover  is  intended  only  for  a  pan  to  catch  the  dirt  which 


UUoU 

OOSOO 


SECTION  Or  FRAME  AMD  COVEF?. 
FIG.  25. — Square  manhole  frame  and  cover. 

falls  through  the  ventilated  outer  cover.  Such  pans,  however, 
are  not  in  general  use.  Ventilated  covers  are  quite  necessary  in 
streets  where  conduits  and  gas  mains  parallel  each  other  in  close 
proximity,  as  without  ventilation  there  is  always  danger  of  gas 
explosions  and  fires  in  the  manholes. 

When  manholes  are  constructed  in  unimproved  streets,  it  is 
well  to  allow  for  any  uncertainty  regarding  the  exact  grade  of  the 
finished  paving.  If,  therefore,  the  roof  is  built  about  4  in.  low 


CONDUIT  AND  MANHOLE  CONSTRUCTION 


53 


and  the  head  casting  is  brought  to  the  surface  by  being  set  on 
bricks  instead  of  directly  on  the  iron  frame,  it  will  allow  a  space 
of  4  in.  for  lowering  the  head  without  disturbing  the  roof  frame  in 


3~^tll i      "5J*""'T*"~6?4~*1-I 8%" 

/w!i^" 


DETAILS  OF  RIB 

FIG.  26. — Manhole  cover  for  asphalt  filling. 

case  the  grade  of  the  street  is  changed  when  permanent  pavement 
is  laid.     Manhole  heads  should  be  set  J^  in.  above  street  grade 
to  prevent  surface  water  draining  into  the  hole. 
Fig.  26    shows  details  of  a  manhole  cover  with  space  at  the 


54       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

top  which  can  be  filled  with  asphalt.  This  cover  is  for  use  in 
locations  where  the  noise  made  by  wagons  running  over  an  iron 
cover  is  objectionable,  or  where  the  authorities  object  to  the 
appearance  of  the  standard  type  of  cover.  Covers  of  this  type 
can  be  developed  to  match  any  kind  of  street  pavement. 

Waterproofing  Manholes. — Few  attempts  seem  to  have  been 
made  to  waterproof  manholes.  In  a  few  special  cases  tarred 
paper  painted  over  in  the  usual  manner  with  waterproofing 
compounds  has  been  employed  to  coat  the  exterior  surface  of  the 
manholes  to  prevent  seeping  of  water.  This  method  of  water- 


;^^^^^^^t^:^^:^^^^':^ 


FIG.  27. — Waterproof  manhole. 

proofing  has  not  been  entirely  satisfactory  owing  to  the  number 
of  corners  and  outlets,  such  as  duct  lines  and  service  connections, 
around  which  it  is  very  difficult  to  make  a  water-tight  joint. 
Concrete  manholes,  in  which  the  concrete  is  mixed  with  some  form 
of  waterproofing  compound,  have  been  built  below  tide  water  and 
made  quite  waterproof.  Probably  the  most  satisfactory  method 
of  securing  this  result  is  to  keep  the  manhole  as  dry  as  possible 
when  pouring  the  concrete,  and  to  use  a  rich  cement  mortar, 
tamping  it  carefully.  A  cement  waterproof  coating  applied  on 
the  inside  of  a  concrete  manhole  has  given  very  good  results. 

Design  of  Manholes  for  Transmission  and  Distribution  Work. 
— Manholes  are  either  two-way,  three-way  or  four-way,  Fig.  28, 
according  to  the  number  of  conduit  outlets,  which  is  determined 


CONDUIT  AND  MANHOLE  CONSTRUCTION 


55 


largely  by  service  requirements.  For  transmission  purposes 
the  two-way  manhole  of  elliptical  or  oblong  octagonal  shape  is 
well-suited,  because  it  provides  sufficient  wall  space  for  the  mak- 
ing of  cable  joints  and  at  the  same  time  eliminates  the  necessity 
for  sharp  bends  in  the  cable.  The  three-way  manhole  practically 
follows  the  lines  of  the  two-way  manhole  on  the  outlet  sides 
excepting  that  the  side  free  from  ducts  is  built  straight.  The 


OVftL 


XOUHDPO  COfttffffS 

FIG.  28.  —  Types  of  manholes. 


7W/ff£  Mt/. 


ideal  shape  of  a  four-way  manhole  is  rectangular,  but  with  the 
opposite  duct  entrances  centrally  displaced.  This  provides 
sufficient  spacing  for  the  training  of  cables  in  all  cases. 

Transformer  Manholes.  —  Frequently  separate  manholes  or 
vaults  are  provided  for  transformers.  These  manholes  are  in- 
stalled, usually,  immediately  adjacent  to  one  of  the  main-line 
manholes,  and  are  very  desirable  when  the  space  in  the  street 
will  allow  construction  of  this  type  to  be  followed.  Manholes 
in  which  there  is  likely  to  be  any  considerable  amount  of  work 


56       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

should  have  a  clear  head  room  of  at  least  6  ft.,  to  provide  working 
space  for  cable  splicers. 

In  the  design  of  manholes  for  the  installation  of  underground 
transformers  consideration  should  be  given  to  the  fact  that 
manholes  must  be  well-ventilated  and  so  constructed  that  they 
can  be  kept  reasonably  free  from  water  during  rain  storms. 
Where  sewer  connections  are  not  possible,  a  dry  well  for  drain- 


FIG.  29. — Transformer  manhole. 

ing  moisture  from  the  bottom  of  the  manholes  is  advocated  as 
an  efficient  means  of  disposing  of  surface  drainage  which  may 
enter  the  manholes.  Natural  ventilation  is  preferred  in  all 
cases  where  the  conditions  are  favorable,  and  sufficient  space 
should  be  allowed  so  that  at  least  3  cu.  ft.  per  kva.  of  transformer 
capacity  is  provided. 

In  general,  where  the  total  capacity  of  the  transformers  in- 
stalled in  a  manhole  does  not  exceed  100  kw.,  the  natural  heat 


CONDUIT  AND  MANHOLE  CONSTRUCTION 


57 


FIG.  30.— Ducts 
grouped  in  center  of 
manhole. 


FIG.  31. — Double  manhole  with  divided 
duct  lines. 


58       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

radiation  from  the  manhole  through  the  ground  is  sufficient  to 
keep  the  transformer  within  safe  temperature  limits.  In  ex- 
treme cases  it  is  advisable  to  provide  artificial  means  of  ventila- 
tion. Many  advantages  are  derived  from  the  use  of  separate 
manholes  for  transformers,  and  in  cases  where  it  is  necessary  to 
install  transformers  of  large  capacity  in  underground  systems  it 
is  frequently  found  advisable  to  arrange  with  large  consumers 


pol         Fool 
oo          too 


Fool 
loon        loo 


FIG.  32. — Double  manhole  with  ducts  separated. 

for  the  installation  of  transformers  in  the  basement  of  buildings 
where  they  are  accessible  for  inspection  and  repairs. 

In  some  cases  it  is  necessary  to  provide  separate  manholes, 
sometimes  called  subsidiary  manholes,  which  are  installed  some 
distance  from  the  main  conduit  line,  either  in  intersecting  streets 
or  underneath  a  sidewalk.  No  cables  pass  through  these  holes 
other  than  the  cables  feeding  the  transformers  installed  therein, 
with  the  result  that  the  heating  effect  is  reduced  to  a  minimum. 

Double  manhole  construction  is  very  desirable  where  it  is 
necessary  to  install  transmission  and  low-tension  power  feeders 


CONDUIT  AND  MANHOLE  CONSTRUCTION  59 

in  the  same  conduit  line.  In  such  installations  a  dividing  wall 
in  the  manhole  permits  the  complete  separation  of  high-tension 
and  low-tension  cables. 

The  ducts  in  some  cases  run  straight  through  the  manhole 
wall,  Fig.  30,  to  the  center  of  the  manhole,  where  the  cables  divide, 
half  going  to  one  side  and  half  to  the  other,  the  cables  being 
racked  on  the  manhole  wall.  Grouping  of  ducts  in  this  manner 
is  very  objectionable  on  account  of  the  sharp  bends  in  the  cable, 
which  may  crack  the  insulation  and  cause  breakdowns.  Rise 
in  temperature  in  one  cable  is  readily  communicated  to  another 
when  the  ducts  are  grouped  in  this  manner. 

The  form  of  construction  adopted  by  the  Niagara  Falls  Power 
Co.  for  one  of  their  recent  installations  is  shown  in  Fig.  31. 
Where  the  space  in  the  street  will  permit  of  this  design,  very 
satisfactory  results  may  be  obtained. 

In  places  where  rock  is  near  the  surface  necessitating  shallow 
excavation  and  affording  excellent  conditions  for  the  -  radiation 
of  heat,  the  type  of  construction  illustrated  in  Fig.  32  will  give 
good  service. 

All  of  these  special  methods  depend  upon  local  conditions  in 
the  streets  and  can  be  used  only  where  foreign  structures  do  not 
interfere. 

In  Fig.  33  is  illustrated  a  typical  design  of  a  two-way  manhole, 
as  recommended  by  the  Committee  on  Power  Distribution  of  the 
Railway  Engineering  Association.  This  type  of  hole  is  well- 
adapted  to  railway  service,  as  it  permits  the  installation  of  heavy 
power  cables  in  almost  a  straight  line,  very  little  bending  of  the 
cable  being  required,  and  the  slack  in  the  manhole  being  reduced 
to  a  minimum.  It  will  be  noted  that  every  third  layer  of  bricks 
is  projected  to  act  as  a  shelf  for  the  cables,  and  while  this  may  be 
good  construction  for  railway  feeders  which  as  a  rule  run  straight 
through  the  manhole,  for  electric  light  and  power  cables,  the 
installation  of  shelves  of  this  type  is  not  so  desirable.  Manholes 
for  electric  light  and  power  cables  frequently  contain  junction 
boxes  and  other  equipment,  and  to  facilitate  their  installation, 
smooth  walls  are  desirable,  the  cables  being  racked  on  the  wall 
by  means  of  portable  hangers  conveniently  arranged.  The 
installation  of  eye-bolts,  as  shown  in  the  sketch,  is  a  very  good 
feature,  as  by  their  use  the  drawing  in  of  cables  is  much  simpli- 
fied. Bolts,  of  this  type  should  be  installed  in  all  manholes,  as  it 


60       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


CONDUIT  AND  MANHOLE  CONSTRUCTION 


61 


62       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


greatly  facilitates  the  rigging  of  cable  tackle  as  described  else- 
where, under  the  heading  of  " Cable  Installation." 

Manholes  of  the  four-way  type,  as  illustrated  in  Fig.  34  are 
usually  placed  at  intersecting  streets  where  two  main  conduit 
lines  cross. 

Concrete  Manhole  Forms. — The  choice  of  forms  will  be  gov- 
erned by  the  character  of  the  work  to  be  done.  Usually  forms 
are  made  of  wood  but  where  there  is  considerable  repetition  and 


G. Board 


FRAME  MADE  IK  4  SECTIONS 


SECTION    A-B 

FIG.  35. — Wood  form  for  concrete  manholes. 

no  obstacles  are  encountered  steel  forms  have  been  used  to  ad- 
vantage. They  may  be  used  a  number  of  times  because  they 
retain  their  shape.  They,  moreover,  produce  a  very  smooth 
finish  on  the  interior  of  the  manhole  wall. 

In  Fig.  35  is  shown  a  manhole  form  constructed  of  wood  so 
designed  as  to  permit  of  the  building  of  manholes  of  various 
sizes  by  simply  changing  the  spacing  between  the  end  sections. 
The  outer  surface  of  the  form  should  be  of  dressed  lumber  in 


CONDUIT  AND  MANHOLE  CONSTRUCTION  63 

order  to  insure  a  smooth  surface  on  the  inside  wall  of  the  man- 
hole. Usually  forms  are  removed  the  second  day  following  the 
placing  of  the  concrete,  but  some  consideration  should  be  given 
to  temperature  conditions  and  the  kind  of  cement  used.  It  will 
take  concrete  considerably  longer  to  set  in  winter  weather  and 
under  unfavorable  atmospheric  conditions,  than  during  the 
summer  months. 

In  order  that  the  forms  may  not  adhere  to  the  concrete  after 
it  has  set,  it  is  customary  to  oil  them  before  the  concrete  is 
placed. 

The  concrete  should  be  of  a  consistency  known  as  "wet  mix- 
ture/7 and  should  be  thoroughly  paddled  and  worked  in  around 
the  form  so  as  to  avoid  a  porous  or  honeycombed  structure. 

The  mixture  most  commonly  used  is  1  part  cement,  3  parts 
sand  and  5  parts  stone.  The  proper  portions  in  any  particular 
case  must  be  determined  by  a  knowledge  of  the  conditions  under 
which  the  structure  is  to  be  installed  and  operated  and  of  the 
quality  of  materials  making  up  the  aggregate. 

After  the  removal  of  the  forms  any  rough  surfaces  should  be 
smoothed  off  and  the  voids  filled  with  cement  mortar.  How- 
ever, if  care  is  taken  in  the  paddling  of  the  concrete,  by  spading 
it  well  around  the  forms,  there  should  be  no  need  of  smoothing 
over  rough  surfaces  after  the  forms  have  been  removed. 

Distribution  Holes. — Service  or  distribution  holes  should  be 
located  at  intervals  of  100  to  150  ft.  between  manholes  in  order 
to  reduce  the  length  of  service  runs.  These  service  holes  should 
be  of  ample  size  to  allow  room  for  the  proper  racking  of  cable  and 
placing  of  subway  boxes.  They  should  be  not  less  than  3  ft. 
square  and  of  sufficient  depth  to  allow  a  man  to  work  in  them. 
In  Fig.  36  two  methods  of  installing  distribution  holes  are  shown. 
Where  the  space  in  the  street  will  allow,  the  holes  should  be  built 
on  the  side  of  the  main  conduit,  as  shown  in  the  illustration. 
In  congested  streets,  however,  this  plan  is  not  always  feasible  and 
under  such  conditions  the  hole  may  be  placed  on  top  of  the  main 
conduit  and  sufficient  ducts  run  therein  for  distribution  cable. 

A  suitable  concrete  foundation  should  be  laid  not  less  than  3 
in.  in  thickness.  The  walls  should  be  built  of  brick  or  concrete, 
depending  on  the  type  of  construction  to  be  used. 

Reinforcing  I-beams  or  old  scrap  rail  are  used  in  the  roof  of 
the  hole  for  supporting  the  iron  frame  or  cover,  which  is  of  the 
same  design  as  those  used  on  manholes,  except  that  it  may  be  of 


64       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

smaller  diameter  to  conform  to  the  size  of  the  hole.  The  type 
and  size  of  the  hole  depends  entirely  upon  the  service  require- 
ments, loads  and  other  local  conditions. 

Cable  Tunnels. — In  some  cities  which  are  divided  into  two  or 
more  parts  by  a  river,  it  has  been  found  expedient  to  build  tunnels 
for  carrying  cables  across  the  river.  The  tunnels  are  built  in 
the  shape  of  an  inverted  U,  with  a  vertical  height  6  ft.  6  in.  in 
the  clear,  and  the  width  6  ft.  with  9-in.  concrete  wall.  The 


FIG.  36. — Methods  of  building  distribution  hole  in  main  conduit  line. 

tunnel  has  a  slope  of  1  or  2  per  cent,  toward  a  sump  at  the  foot 
of  one  of  the  shafts  so  that  the  tunnel  can  be  pumped  out  pre- 
liminary to  cable  pulling.  At  each  end  of  the  tunnel  is  a  shaft 
6  ft.  6  in.  internal  diameter,  with  15-in.  walls  built  of  concrete. 
At  the  upper  end  of  each  shaft  is  a  manhole  which  forms  the 
terminus  of  the  conduits  leading  to  and  from  the  tunnel.  It  is 
advisable  to  have  the  tunnel  shaft  extend  2  ft.  above  the  bottom 
of  the  manhole  for  convenience  in  working  and  as  a  protection 


CONDUIT  AND  MANHOLE  CONSTRUCTION 


65 


to  the  workmen.  A  permanent  galvanized-iron  grating  is  placed 
over  the  unoccupied  portion  of  the  upper  end  of  the  shaft  so  as 
to  prevent  accidents. 

On  completion  of  the  tunnel  a  standard  conduit  is  installed  in 
a  horizontal  position,  and  in  each  of  the  shafts,  leaving  a  gap  at 
the  junction  of  the  tunnel  with  the  shafts  to  allow  for  proper 
training  of  the  cables.  This  junction  should  be  built  with  a  curve 
having  a  radius  of  about  6  or  8  ft.,  to  give  proper  working  space 
and  permit  the  cable  to  be  installed  with  easy  curves.  The 
vertical  conduit  in  the  shafts  can  be  built  with  single-duct, 
vitrified  tile,  fiber  pipe  or  stone  conduit.  Tee  irons  are  fitted 
into  the  shafts  at  intervals  of  about  2  ft.,  so  as  to  leave  a  clear 


TUNNEL   SHAFT 


VERTICAL    CONDUIT 


FIG.  37.— Cable  tunnel  shaft. 


space  in  the  center  of  the  shaft  about  2  ft.  wide.  With  the 
dimensions  given  for  the  shaft  about  35  or  40  ducts  can  be 
installed  between  the  tee  irons  and  the  shafts  on  each  side. 

A  brick  or  concrete  pier  under  the  curve  in  the  cables  at  the 
lower  end  of  the  shaft  will  support  a  considerable  portion  of  the 
weight  of  the  vertical  cable.  Some  additional  means  of  support 
for  each  cable  should  be  installed  at  the  top  of  the  shaft.  Care 
should  be  exercised  to  avoid  clamping  the  cable  too  tightly  or 
placing  too  great  a  strain  on  the  lead  sheath. 

Fig.  37  illustrates  the  method  of  training  cable  in  the  manhole 
over  a  tunnel  shaft. 

5 


66       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

The  telephone  company  in  Chicago  has  used  iron  pipes  exclu- 
sively for  the  vertical  conduits  in  shafts  and  has  made  the  connec- 
tions between  these  vertical  pipes  and  the  conduits  in  the  tunnel 
with  bends  of  6  or  8  ft.  radius  in  such  a  manner  that  the  duct  is 
continuous  from  the  top  of  one  shaft  to  the  top  of  the  other. 
Copper  lead-wires  are  installed  at  the  time  that  the  conduit  is 
built,  so  as  to  avoid  difficulty,  which  might  be  experienced  with 
iron  wires.  This  provision  allows  the  pulling  in  of  cables  at  any 
future  time  without  pumping  out  the  tunnel,  and  at  the  same  time 
eliminates  all  joints  from  the  bottom  of  the  shafts.  It  is  probable 
that  the  same  scheme  could  be  used  with  smaller  cables  for  elec- 
tric light  and  power  purposes,  but  this  is  not  the  usual  practice. 

A  useful  auxiliary  in  connection  with  such  tunnels  is  a  motor- 
driven  pump  of  about  15  hp.  capacity  for  removing  the  water 
from  the  tunnel.  Such  pumps  can  be  obtained  with  either  a 
direct-current  or  alternating-current  motor,  and  can  be  readily 
lowered  in  the  clear  space  in  the  tunnel.  These  outfits  are 
preferably  built  with  a  vertical  shaft,  and  for  convenience  in 
assembling,  are  made  in  two  parts. 

The  tunnel  shaft  should  be  erected  from  25  to  50  ft.  away  from 
the  river  edge,  depending  on  local  conditions.  Where  the  river 
bank  consists  of  filled  ground,  it  may  be  necessary  to  use  a  steel 
shield,  extending  into  the  impervious  clay  below  the  river.  With 
a  stiff  clay  the  depths  of  the  tunnel  below  the  lowest  portion  of  the' 
river  should  be  about  15  or  20  ft.  If  there  is  not  sufficient  depth 
of  clay  above  the  rock  to  give  this  amount  of  clearance  to  the 
river,  the  tunnel  should  be  built  in  the  rock.  In  Chicago  these 
tunnels  are  located  at  least  15  ft.  below  the  surface  of  the  rock, 
so  as  to  avoid  the  danger  of  letting  in  any  water  while  blasting. 

The  cost  of  such  a  tunnel,  if  in  clay,  will  be  about  $25  to  $35 
per  lin.  ft.,  plus  $50  to  $60  per  ft.  for  the  shaft.  If  built  in 
rock  the  expense  will  be  increased  about  50  per  cent. 

These  prices  do  not  include  manholes  at  the  top  of  the  shafts, 
or  the  conduits  in  the  tunnel  and  shaft. 

Very  little  water  has  been  encountered  in  building  tunnels  in 
hard  blue  clay.  Considerable  water  is  usually  present  in  build- 
ing tunnels  through  rock,  as  the  surrounding  rock  is  somewhat 
shattered  by  the  blasting,  opening  up  water  seams,  which  adds 
considerable  difficulty  to  the  construction  of  the  tunnel.  When 
completed,  the  tunnels  through  clay  are  generally  dry,  while 
those  through  rock  are  somewhat  leaky. 


CONDUIT  AND  MANHOLE  CONSTRUCTION  67 

Slight  leaks  that  do  not  interfere  with  the  construction  work 
or  prevent  pumping  the  tunnel  out  for  cable  installations  are 
not  objectionable  as  it  is  the  practice  to  allow  the  tunnel  to  fill 
up  with  water  after  the  cables  are  installed.  Tunnels  built  in  the 
manner  just  described  have  been  in  service  for  as  much  as  12 
years  and  no  serious  operating  difficulties  have  been  experienced. 

Specification  and  Contract. — It  is  very  often  desirable  to  have 
subway  construction  work  done  by  an  outside  contractor,  and 
while  contracts  are  frequently  drawn  by  engineers,  it  is  necessary 
that  the  subject  matter  be  in  legal  form.  Specifications  should 
be  clear  and  so  written  that  the  precise  meaning  of  each  sentence 
is  understood  and  that  no  doubt  exists  in  the  mind  of  the  con- 
tractor as  to  their  intent.  It  is  not  necessary  in  preparing  a 
specification  to  model  the  language  after  that  used  in  many  legal 
documents,  but  the  specifications  should  be  complete  in  every 
detail  and,  as  far  as  possible,  the  use  of  long  or  involved  sentences 
should  be  avoided.  This  is  particularly  desirable  in  view  of  the 
fact  that  such  specifications  are  often  placed  in  the  hands  of  con- 
struction foremen  whose  knowledge  of  legal  phraseology  is  limited. 
Short  and  simple  wording  is  preferable  and  it  should  be  the  aim 
of  the  engineer  to  make  the  language  crisp  and  concise,  rather 
than  to  produce  a  literary  masterpiece. 

The  specifications  should  describe  in  detail  the  work  to  be 
covered  and  should  give  directions  as  to  how  it  is  to  be  done. 
Specifications  are  usually  accompanied  by  plans  of  the  work  and 
the  drawings  should  be  mentioned  in  the  specification  giving  the 
number,  date  and  title  of  the  drawing.  Contractors  are  usually 
required  to  give  a  bond  which  provides  for  the  payment  to  the 
owner  of  an  indemnity  in  case  the  contractor  fails  to  live  up  to 
a  part  or  all  of  his  agreement.  While  there  are  many  forms  of 
specifications  in  use,  the  following  specimens  cover  most  classes 
of  conduit  and  manhole  construction. 

SPECIFICATION  AND  CONTRACT 

THIS  AGREEMENT,  made  and  concluded  this  day 

of in  the  year between  

a  Corporation  of  the  State  of of  the  first  part,  and 

of  the  State  of  ,  of  the  second 

part: 

WITNESSETH:  That  the  said  party  of  the  second  part  (hereinafter 
designated  Contractor)  has  agreed  and  by  these  presents  does  agree  with  the 


68       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

said  party  of  the  first  part  (hereinafter  designated  Company)  for  the  con- 
sideration hereinafter  mentioned  and  under  the  penalty  expressed  on  a  bond 
bearing  even  date  with  these  presents,  and  hereunto  annexed,  at  his  own 
proper  cost  and  expense,  to  do  all  the  work  and  furnish  all  the  material  called 
for,  in  the  manner  and  under  the  conditions  set  forth  in  the  following  speci- 
fications, and  the  attached  plans,  which  constitute  a  part  of  this  contract. 
It  is  understood  that  the  work  covered  by  this  contract  is  intended  for 

1.  Wherever  the  term  "Engineer"  appears  it  shall  mean  the  engineer 
employed  by  the  company  and  in  charge  of  the  work  and  construction  to  be 
done  hereunder. 

2.  The  subways  for  electrical  wires  and  cables  covered  by  this  contract, 
and  these  specifications  and  plans  herewith  attached,  are  to  be  built  in  the 

following  streets,  alleys,  lanes  and  public  places  of  the  city  of 

in  the  State  of  .  .  viz :   . 


and  in  such  other  streets,  alleys,  lanes  and  public  places  in  said  city  of 

as  may  hereafter  be  designated  by  the  company. 

The  foregoing  schedules  of  streets  and  alleys  contain  those  upon  which 
are  to  be  located  the  conduits,  manholes  and  service  boxes  that  it  is  now 
intended  to  be  built,  but  it  is  agreed  that,  during  the  progress  of  the  work, 
any  additional  extensions  or  subtractions  to  the  conduits,  manholes,  serv- 
ice boxes  or  laterals  shall  be  constructed  by  the  contractor  as  required 

by The  terms  and  conditions  of  this  agreement  shall  apply 

to  and  cover  all  such  conditions,  provided  that  such  work  is  reasonably 

similar  to  that  which  is  now  specified.     It  is  also  agreed  that   

may  decrease  the  amount  of  work  in  any  way  it  shall  deem  advisable  with- 
out becoming  liable  to  the  contractor  for  any  compensation  or  damage  for 
such  change,  provided  shall  notify  the  contractor  in  writ- 
ing before  instructions  are  given  to  commence  the  portion  of  the  work.  If 
said  change  in  combination  of  ducts  and  trench  feet  now  shown  on  plans 
herewith  attached,  should  be  altered  so  as  not  to  be  substantially  similar  to 
the  schedule  figured  on,  then  a  revised  figure  is  to  be  agreed  upon  and  made 
the  basis  upon  which  payment  is  to  be  made. 

3.  Due  notice  will  be  given  by  the  company  as  to  the  location  of  certain 
divisions  of  the  work  and  when  same  shall  be  commenced,  in  order  to  insure 
perfect  cooperation  between  the  company  and  the  contractor  in  prosecuting 
the  work  without  delay. 

4.  The  company  will  obtain  the  rights-of-way  and  street  permits  needed 
for  the  prosecution  of  the  work  contemplated  under  this  agreement. 

5.  The  work  to  be  done  by  the  contractor  is  to  include  the  furnishing  of 
all  materials  (except  the  conduit,  service-box  castings,  manhole  castings, 
eye  beams,  expanded  metal  for  manhole  roofs,  and  form  for  drain  opening  in 
floor  of  manhole),  all  labor,  tools,  night  lights,  bridging,  guard  rails,  shoring, 
and  so  forth.     The  contractor  is  also  to  remove  the  pavements  along  the 
route  of  the  work  to  excavate  for  trenches  and  manholes,  and  to  refill  the 
same,  and  to  repave  the  streets  in  a  complete  and  workmanlike  manner  in 
accordance  with  the  original  specifications  under  which  the  street  pavement 
is  laid.     For  refilling  the  trenches  the  best  and  most  substantial  part  of  the 


CONDUIT  AND  MANHOLE  CONSTRUCTION  69 

materials  excavated  shall  be  used,  it  shall  be  thoroughly  tamped,  rammed, 
rolled  or  flushed,  as  may  be  deemed  necessary  to  the  engineer  or  required 
by  the  city  authorities,  and  shall  be  done  with  the  proper  tools  and  in  a  man- 
ner to  prevent,  as  far  as  possible,  a  settlement  of  the  earth  after  completion. 

6.  The  backfilling  of  the  trenches  shall  be  done  according  to  the  regula- 
tions of  the  city  of  and  the  requirements  of  the  city  civil 

engineer  and  all  new  or  other  material  required  for  this  purpose  and  the  haul- 
ing thereof  shall  be  furnished  and  done  by  the  contractor  at  his  expense. 
The  contractor  shall  furnish  all  materials  and  labor  required  for  installing 
walls  and  floors  of  manholes  and  labor  for  setting  forms  for  the  drain  open- 
ing in  floor  of  the  manholes  and  shall  set  manhole  and  service-box  covers. 

7.  The  work  is  to  be  done  under  the  line  of  streets,  alleys,  lanes  and  public 
places  as  designated  by  the  engineer. 

8.  The  trenches,  manholes,  and  service  boxes  are  to  be  located  according 
to  the  position  assigned  by  the  engineer  in  charge  of  work  under  approval 
of  the  city  authorities. 

9.  The  work  performed  and  material  supplied  under  this  specification 
shall  be  subject  to  inspection  of  the  engineer  of  the  company,  and  the 
contractor  must  remove  and  make  good,  at  his  own  cost,  all  material  that 
does  not  fully  comply  with  the  specification.     The  decision  of  the  engineer 
shall  be  final  on  all  matters  under  this  contract. 

10.  The  company  shall  maintain  engineering  inspection  of  the  work  dur- 
ing its  progress,  and  should  the  contractor  fail  to  fulfill  the  specifications  or 
any  portion  of  the  contract,  or  in  any  particular  fail  to  perform  the  work 
herein  specified,  he  shall  be  given  a  written  notification  of  such  failure,  and 
must  correct  the  same  and  proceed  with  the  work  within  twenty-four  (24) 
hours  of  such  notice,  and  his  failure  to  correct  the  faults  or  to  so  proceed  with 
the  work  shall  be  deemed  sufficient  cause  for  voiding  of  the  contract  which 
the  company  may  at  its  option  do. 

11.  Should  the  contractor  cease  work  hereunder  for  ten  (10)  consecutive 
days  unless  prevented  from  proceeding  therewith  from  stress  of  weather  or 
unavoidable  casualty  or  accidents,  or  by  act  or  default  of  the  company,  the 
company  may,  at  its  option,  treat  the  work  and  contract  as  abandoned  and 
proceed  as  is  herein  provided  to  be  done  in  case  of  such  abandonment. 

12.  Should  the  contractor  abandon  said  work,  or  if  this  contract  should  be 
terminated  by  the  company  as  above  provided,  all  material  delivered  and  on 
the  line  of  the  work  shall  become  the  property  of  the  company,  and  such 
material  and  all  tools,  implements,  vehicles  and  machinery  along  the  line  of 
the  work  may  be  used  by  the  company  or  its  agents  or  employees  to  complete 
the  construction  provided  for  by  its  contract. 

13.  If  the  contractor  shall  refuse  or  neglect  to  proceed  immediately  with 
the  correction  of  any  default,  or  to  proceed  with  the  work  as  required  by  the 
engineer,  said  company  may  employ  men  and  teams  and  purchase  material 
to  effect  the  requisite  corrections  or  to  complete  the  work  at  the  expense  of 
the  contractor,  the  cost  thereof  to  be  deducted  from  any  moneys  due  to  the 
contractor  or  to  be  recovered  from  him  and  the  sureties  on  his  bond. 

14.  In  case  the  contractor  shall  not  be  present  upon  the  work  at  any  time 
when  it  may  be  necessary  to  give  instructions,  the  foreman  in  charge  for  the 
time  being  shall  receive  and  obey  any  orders  that  the  engineer  may  give. 


70       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

15.  The  engineer  may  require  the  discharge  from  the  work  of  any  incom- 
petent or  unfaithful  employees  who  may  neglect  to  execute  the  work  in 

.  accordance  with  the  specifications  and  the  direction  of  the  engineer,  and  the 
contractor  shall  not  again  employ  such  person  on  any  part  of  the  work  with- 
out the  consent  of  the  engineer. 

16.  The  handling  of  materials  and  all  work  relating  thereto  must  be  done 
in  compliance  with  the  regulation  established  by  the  city  authorities  of  the 

city  of  The   contractor   shall   immediately   remove  all 

surplus  material  as  fast  as  the  work  is  finished  and  dispose  of  same  at  his 
own  cost. 

17.  The  contractor  shall  furnish  all  necessary  watchmen,  place  sufficient 
and  proper  guards  for  the  prevention  of  accident,  and  shall  put  up  and 
keep  at  night  suitable  and  sufficient  danger  lights  and  barricades  as  required 
by  the  ordinance  of  said  city,  and  shall  indemnify  and  save  harmless  the 
company,  its  officers,  agents  and  servants  against  and  from  all  damages, 
cost  and  expense,  which  they  may  suffer,  or  to  which  they  may  be  put  by 
reason  of  injuries  to  person  or  property  of  another,  resulting  from  negligence 
or  carelessness  or  accident  on  the  part  of  said  contractor. 

18.  The  contractor  must  furnish  all  necessary  guard  rails,  staging  or 
bridging  that  may  be  necessary  to  cover  over  the  trenches  so  as  to  not  ob- 
struct public  travel  at  crossings. 

19.  If,  in  the  excavation  of  trenches  a  water  main  or  pipe  service,  a  line 
of  gas  pipe,  or  any  private  or  public  underground  service  of  any  character 
is  encountered,  all  necessary  protection  from  injury  thereof  must  be  provided 
by  the  contractor,  and  if  necessary  to  make  any  changes  thereto  same  must 
be  done  entirely  by  the  contractor  and  to  the  approval  of  the  owners;  pay- 
ment for  same  should  be  agreed  upon  in  writing. 

20.  The  contractor  must  assume  all  responsibility  for  damage  of  any  kind 
caused  by  his  employees  to  any  sewer,  gas  pipe,  conduit  or  other  underground 
system  and  must  make  such  damage  good  at  his  own  cost  and  expense.     The 
repairs  must  be  satisfactory  to  the  owners. 

21.  The  contractor  will  assume,  and  shall  be  held  liable  for,  any  damage 
to  property,  or  any  accident  to  men  or  material,  connected  with  the  work 
described  in  these  specifications  which  may  occur  prior  to  the  final  comple- 
tion of  the  work  and  its  acceptance. 

22.  The  contractor  shall  pay,  discharge  and  satisfy  all  claims  for  material 
furnished  and  labor  done  in  carrying  out  this  contract  and  shall  fully  protect 

the  company  and  from  all  such  claims  or  liens  on  account 

thereof  and  the  bond  to  be  given  by  the  contractor  shall  comply  with  this 
clause. 

23.  The  contractor  is  to  furnish  such  a  force  of  men  and  teams,  and  such 
labor-saving  devices,  such  as  concrete  mixers,  rock  drills,  tools,  machinery, 
and  so  forth,  as  in  the  judgment  of  the  engineer  is  necessary  to  prosecute 
the  work  with  satisfactory  speed. 

24.  If  the  contractor  does  not  prosecute  said  work  as  rapidly  as  in  the 
opinion  of  the  engineer  he  should,  the  contractor  shall  employ  and  put 
to  work  so  many  additional  men,  teams  and  labor-saving  devices  as  the 
engineer  may  require,  and  if  the  contractor  fails  to  do  so,  the  company  may 


CONDUIT  AND  MANHOLE  CONSTRUCTION  71 

employ  and  put  to  work  such  additional  men,  teams  and  labor-saving 
devices,  and  shall  charge  the  contractor  with  the  cost  thereof. 

25.  The  work  shall  be  prosecuted  in  such  a  manner  as  to  cause  as  little 
inconvenience  as  possible  to  public  travel  and  to  property  owners  on  the 
streets,  alleys,  lanes  and  public  places  where  the  conduit  is  laid.     The  order 
in  which  the  work  shall  be  prosecuted  and  the  sections  which  shall  be  first 
laid  will  be  indicated  by  the  engineer.     The  work  shall  be  commenced  within 

days  of  the  execution  of  the  contract  and  completed  on  or 

before 

26.  The  paving,  if  any,  removed  from  the  trench,  shall  be  neatly  and 
compactly  piled  along  the  trench  on  the  curb  line,  except  in  cases  of  cross 
streets,  when  a  modified  disposition  may  be  advisable,  but  the  flow  of  water 
in  gutters  or  drains  shall  not  be  obstructed. 

27.  All  pavements  disturbed  by  the  contractor  must  be  replaced  by  him 
with  a  paving  of  the  same  character  and  equal  quality  and  he  must  give 
bond  guaranteeing  the  maintenance  of  the  pavement  during  the  term  of 
one  year  from  the  completion  and  acceptance  of  the  work  to  be  done  under 
this  contract,  all  new  material  required  to  replace  pavement  as  aforesaid 
shall  be  furnished  by  the  contractor.     Where  it  is  necessary  to  disturb 
pavements  which  have  been  laid  under  a  guaranty  the  contractor  is  to  ar- 
range with  the  municipal  authorities  to  have  this  pavement  replaced  under 
the  original  guaranty.     In  such  case  the  contractor  is  to  make  temporary 
repairs  to  the  pavement,  which  he  shall  maintain  for  a  period  of  at  least  sixty 
(60)  days  or  until  such  time  that  the  pavement  is  permanently  restored  to 
its  originaUcondition. 

28.  All  excavations  and  openings  of  streets  must  be  done  in  compliance 
with  the  regulations  established  by  the  city  authorities  of  the  city  of 

29.  The  engineer  will  give  any  explanations  or  directions  required  to 
complete  or  give  proper  and  due  effect  to  the  provisions  of  the  specifications, 
and  will  appoint  such  assistants  and  inspectors  as  he  may  deem  necessary 
to  secure  compliance  with  the  same. 

30.  The  engineer  shall  determine  all  questions  that  may  arise  in  regard 
to  lines,  levels,  locations,  dimensions,  materials  and  workmanship. 

31.  If,  in  the  opinion  of  the  engineer,  it  is  necessary  to  make  changes  in 
said  plans,  the  same  may  be  made  by  him  and  the  work  shall  be  done  in 
accordance  with  the  plans  as  changed,  and  the  contractor  shall  not  be  en- 
titled to  extra  pay  therefor,  unless  the  engineer  shall  certify  that  work  re- 
quired by  the  changes  is  in  addition  to,  or  of  a  different  and  more  costly 
character  than,  that  embraced  in  the  original  plans,  and  such  extra  pay 
shall  be  agreed  upon  before  the  extra  work  is  done. 

32.  The  trench  shall  be  excavated  by  the  contractor  to  such  width  and 
depth  as  may  be  required  to  receive  the  number  of  ducts  required  by  the 
company,  as  designated  by  the  engineer.     There  shall  be  an  allowance  of 
three  (3)  inches  for  work  space  on  each  side  of  the  completed  duct.     The 
grade  of  the  trench  shall  be  such  as  will  conform  to  the  requirements  of 
the  street  route  for  making  a  continuous  line  of  conduit  from  manhole  to 
manhole,  and  where  the  obstructions  or  other  underground  service  are  met 
with,  the  excavation  shall  be  done  as  far  as  may  be  required  to  afford  facilities 
for  laying  of  conduits  around,  under  or  over  such  obstructions.     Should  it 


72       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

be  found  necessary  for  the  conduit  to  straddle  gas  or  water  pipes  or  any 
other  obstructions,  either  vertically  or  horizontally,  the  excavation  must 
be  made  accordingly,  and  in  these  details,  as  the  inspecting  engineer  on  the 
work  may  direct. 

LOOSE  DIRT 

33.  Loose  dirt  on  bottom  of  trenches  is  to  be  tamped  solid  previous  to 
laying  conduits,  and  any  sharp  stones  or  rocks  which  are  encountered  in 
bottom  of  trench,  or  in  filling  dirt,  must  be  removed  to  prevent  injuring 
conduits. 

34.  The  sides  of  the  trenches  will  be  vertical,  and  wherever  required  the 
contractor  must  shore  the  trenches  to  prevent  caving.     The  contractor 
must  assume  all  responsibility  for  the  safety  of  -the  work  and  no  extra  charge 
will  be  recognized  for  the  shoring  and  other  protection  of  the  work.     During 
the  progress  of  the  work  the  trenches  must  be  kept  absolutely  free  from 
water.     All  pumping  that  may  be  necessary  must  be  done  by  the  contractor 
without  extra  cost. 

LAYING 

35.  Conduits  to  be  laid  so  as  to  break  joints  and  true  to  line,  so  that  no 
shoulders  or  offsets  shall  be  formed  in  the  bores,  to  be  built  up  in  tiers  to  the 
required  arrangement  and  bedded  in  cement  mortar.     Conduits  must  be 
laid  to  drain  to  the  manholes.     Conduits  may  be  laid  to  vary  slightly  from 
a  straight  line,  providing  there  are  no  "sags"  or  "pockets"  which  will  not 
drain  themselves.     Where  multiple-duct  is  used  the  joints  are  to  be  thor- 
oughly protected  by  a  strip  of  tarred  burlap  not  less  than  six  (6)  inches 
wide  and  long  enough  to  go  around  the  conduit  in  a  continuous  piece  and 
overlapping  on  the  top  by  not  less  than  four  (4)  inches.     This  burlap  must 
be  applied  before  applying  the  cement  mortar.     A  mandrel  shall  be  drawn 
through  each  duct  as  work  progresses.      Conduits  must  be  laid  with  at 
least  thirty  (30)  inches  between  the  top  layer  of  ducts  and  the  finished 
street  surface.     This  distance  may  be  modified  by  the  engineer  of  the  com- 
pany, if  the  exigencies  of  the  work  demand  it  and  the  engineer  thinks  it 
advisable.     Wherever  it  may  be  deemed  expedient  or  necessary  by  the  com- 
pany's engineer,  ducts  shall  be  reamed  by  the  contractor  in  a  manner 
approved  by  the  company's  engineer  and  at  the  sole   expense   of   the 
contractor. 

MORTAR 

36.  Mortar  for  laying  conduit  to  be  mixed  of  one  (1)  part  of 

cement,  to  two  (2)  parts  clean  sharp  sand,  and  must  be  used  within 

after  being  mixed. 

CONCRETE 

37.  A  concrete  bed  three  (3)  inches  in  depth  and  of  width  sufficient  to 
extend  three  (3)  inches  beyond  the  sides  of  the  conduits  must  be  placed  on 
the  bottom  of  the  trenches  and  brought  to  smooth  even  surface  of  uniform 
grade.     After  the  conduits  are  in  place,  three  (3)  inches  of  concrete  must  be 


CONDUIT  AND  MANHOLE  CONSTRUCTION  73 

placed  on  the  sides  and  top.  If  the  space  between  sides  of  conduits  and  sides 
of  trench  is  too  great  to  be  entirely  filled  with  concrete,  and  boards  are  used, 
these  must  be  left  in  place  or  else  withdrawn  so  as  not  to  disturb  concrete 
or  earth  filling  and  in  a  manner  acceptable  to  the  engineer.  All  concrete 

to  be  made  of  one  (1)  part  cement,  two  (2)  parts  clean  sharp 

sand,  and  five  (5)  parts  of  screened  gravel.  Cement  and  sand  to  be  first 
thoroughly  mixed  dry,  then  a  sufficient  quantity  of  water  added  to  form  a 
soft  mortar;  the  gravel  to  be  afterward  added  and  thoroughly  mixed.  The 
concrete  when  placed  in  trench  to  be  tamped  till  water  flushes  to  the  sur- 
face. The  placement  of  concrete  to  be  so  conducted  as  not  to  disturb  the 
conduits  while  mortar  is  setting. 

38.  Service  laterals  shall  be  installed  by  the  contractor  at  the  places 
designated  by  the  engineer  and  run  into  the  basement  or  cellar.     These 
laterals  will  be  run  with  single  conduit  and  under  same  specifications  as  the 
other  conduit  work. 

PLUGS 

39.  Wherever  and  whenever  work  is  suspended,  the  open  end  of  all  ducts 
must  be  plugged  with  hard-wood  plugs  conforming  accurately  to  the  shape 
of  the  duct,  and  at  the  larger  end  at  least  one-quarter  (^)  of  an  inch  greater 
in  dimension  than  the  duct. 

BLASTING 

40.  Where  blasting  is  required,  moderate  charges  of  explosive  must  be 
used,  and  the  blast  covered  with  heavy  logs  and  chains,  or  other  measures 
taken  to  protect  life  and  property.     Excavation  of  ledge,  rock  or  such  boul- 
ders as  may  contain  ten  (10)  cubic  feet  or  more  will  be  subject  to  extra  pay- 
ments at  rates  hereinafter  named. 

ROBBING 

41.  Upon  completion  of  the  entire  work  and  before  acceptance  by  the 
company,  the  contractor  will  be  required  to  pass  through  each  duct,  from 
manhole  to  manhole,  an  iron  or  iron-shod  mandrel  conforming  in  shape 
to  that  of  the  duct,  and  of  not  more  than  one-quarter  (%)  inch  smaller  di- 
mension.    Any  obstruction  to  the  free  passage  of  the  mandrel  through  the 
ducts  must  be  removed  by  the  contractor  at  his  own  expense. 


EXTRAS 

42.  No  claim  for  extra  payment  is  to  be  made  except  for  extra  work 
done  in  obedience  to  written  orders  from  the  engineer  approved  by  the 
company. 

MANHOLES 

43.  Manholes  and  service  boxes  will  be  as  shown  on  accompanying  plans, 
unless  otherwise  directed  by  the  inspecting  engineer.     They  are  to  be  con- 
structed of  the  best  cement.     Concrete  mixed  over  one  (1) 

hour,  or  that  has  commenced  to  set,  shall  not  be  retempered  or  used.     All 


74       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

manholes  shall  be  drained  by  means  of  a  round  opening  located  in  the  floor 
of  the  manholes  at  such  points  as  shall  be  designated  by  the  engineer,  and  the 
form  for  this  opening  will  be  furnished  by  the  company.  All  service  holes 
must  have  drain  tubes,  supplied  by  the  company,  installed  in  the  walls  of 
same,  at  points  designated  by  the  engineer  of  the  company. 

MANHOLE  FRAMES 

44.  Manhole  and  service-hole  frames  and  covers  to  be  as  per  plans. 
Each  manhole  and  service-hole  frame  when  set  shall  be  bedded  in  cement 
mortar  and  must  be  set  to  a  line  not  exceeding  one-half  (££)  inch  above  grade 
of  finished  pavement,  and  shall  not  in  any  event  be  below  said  grade  after 
settlement. 

MEASUREMENT 

45.  The  number  of  duct  feet  to  be  paid  for  under  these  specifications  shall 
be  according  to  the  actual  measurements  of  the  finished  work  from  face  to 
face  of  manhole  walls.     The  manhole  and  service  manholes  will  be  paid 
for  at  so  much  per  manhole  complete.    Service  laterals  will  be  paid  for  accord- 
ing to  the  actual  measurements  of  the  finished  work  from  face  of  service 
box  or  manhole  to  face  of  basement  or  cellar  wall  or  floor  line  where  there  is 
no  basement  or  cellar.     Where,  owing  to  obstructions,  manholes  cannot  be 
built  to  a  specified  dimension,  and  in  order  to  get  the  desired  working  space, 
it  is  necessary  that  the  manhole  be  constructed  of  a  shape  and  size  not 
shown  on  the  plans;  the  contractor  is  to  be  paid  at  a  unit  price  per  cubic 
yard  of  brick  work  or  concrete,  in  the  sides,  top  and  bottom  of  the  hole. 

46.  Contractor  shall  use  every  care  hi  handling  conduit,  and  any  damage 
through  carelessness  on  his  part  to  be  replaced  at  his  expense. 

47.  Any  work  proving  defective  within  one  (1)  year  after  completion  of 
the  work,  if  due  to  the  use  of  poor  material  or  faulty  construction,  or  both, 
shall  be  replaced  free  of  charge  by  the  contractor. 

48.  All  walls  when  broken  through  in  installing  laterals  as  provided  for 
in  Paragraph  38,  shall  be,  by  the  contractor  at  his  own  expense,  left  in  as  good 
condition  as  they  were  before  such  laterals  were  installed. 

49.  Test  pits  shall  be  put  down  at  the  contractor's  expense  wherever 
thought  desirable  and  of  such  size  as  is  necessary  to  determine  the  feasible 
location  for  the  trench,  manholes  and  service  holes. 

50.  Particular  care  shall  be  taken  not  to  obstruct  access  to  fire  hydrants, 
manholes,  catch  basins  and  grates  belonging  to  the  city  or  any  other  cor- 
poration or  individual  in  the  vicinity  of  the  work  and  to  arrange  free  passage 
ways  for  the  fire  department. 

51.  Such  ducts  as  may  be  deemed  necessary  for  the  installation  of  the 
said  conduit  system  across  any  canal  or  river  shall  be  installed  in  proximity 
to  the  various  bridges  crossing  the  canal  or  river  at  such  points  as  may  be 
designated  and  approved  by  the  company's  engineer. 

BOND 

52.  The  contractor  will  be  required  to  execute  a  bond  in  the  sum  of 

with  such  sureties  as  shall  be  approved 

by  the  company. 


CONDUIT  AND  MANHOLE  CONSTRUCTION  75 

53.  The  undersigned  contractor  hereby  proposes  to  build  subway  for 
the  undersigned  as  itemized  in,  and  shall  do  so  all  in  accordance  with  the 
foregoing  specifications  and  the  attached  plans,  and  agrees  to  receive  the 
following  prices  in  full  compensation  for  furnishing  all  materials  (including 
or  excepting  manhole  castings)  and  all  labor  necessary  for  the  complete 
installation : 

For    4-duct  subway  under  (?)  pavement,  per  duct  foot 

For    6-duct  subway  under  (?)  pavement,  per  duct  foot 

For  12-duct  subway  under  (?)  pavement,  per  duct  foot 

For  24-duct  subway  under  (?)  pavement,  per  duct  foot 

For  manholes  under  (?)  pavement,  each 

NOTE. — Above  may  be  specified  the  various  sizes  of  conduits  and  man- 
holes, as  well  as  kinds  of  pavement  under  which  they  are  constructed. 

For  service  laterals  under  (?)  pavement,  per  foot 

The  price  for  extra  work  is  as  follows: 

Per  cubic  yard  for  dirt  excavation  and  removal. 

Per  cubic  yard  for  dirt  excavation  and  refilling : 

Per  square  yard  for  repaving 

(Here  mention  various  kinds  of  paving  work  to  be  done.) 

Per  cubic  yard  of  concrete  in  place 

Per  cubic  yard  for  rock  excavation  and  removal 

Per  cubic  yard  for  clean,  sharp  building,  sand,  delivered  on  the  work 

Per  barrel  of  cement,  delivered  on  the  work 

Per  cubic  yard  for  clean,  freshly  crushed  stone,  delivered  on  the  work 

Per  thousand  brick,  delivered  on  the  work 

Per  thousand  brick,  laid  in  place 

Per  day  of  ten  (10)  hours  for  double  team,  truck  and  driver 

Per  day  of  ten  (10)  hours  for  common  labor 

The  undersigned  company,  by  its  duly  authorized  officer  or  representative, 
hereby  accepts  the  proposal  of  the  undersigned  contractor,  and  agrees  that 
it  will  cause  to  be  made  each  month,  approximate  monthly  statements  of 
the  work  done  and  material  delivered,  and  it  will  pay  to  the  contractor  on  or 

before  the  day  of  each  month per  cent. 

(%)  of  the  value  of  the  estimated  work  done  and  materials  delivered  during 
the  next  previous  month.  The  company  further  agrees  to  pay  to  the  con- 
tractor at  or  before  the  expiration  of (  )  days  after  the 

work  has  been  completed  in  accordance  with  the  agreement  and  formally 
accepted  by  the  company,  the  whole  amount  of  money  then  remaining  due. 

IN  WITNESS  WHEREOF,  the  undersigned  have  hereunto  set  their 
hands  and  seals  the  year  and  day  first  above  mentioned. 

FORM  OF  BOND 

KNOW  ALL  MEN  BY  THESE  PRESENTS:  That  we 

a  corporation  of  the  State  of   as  principal,  and 

as  sureties,  are  hereby  held  and  firmly  bound 

unto  a    corporation    of    the    State    of 


76       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

in    the    sum     of  Dollars 

(S       )  lawful  money  of  the  United  States  of  America,  to  be  paid  to  the  said 

or  its   certain  attorney,   its  successors  and 

assigns  for  which  payment,  well  and  truly  made,  we  bind  ourselves,  our  heirs, 
executors  and  administrators,  jointly  and  severally,  firmly  by  these  presents: 

Sealed  with  our  seals,  dated  the  day  of  

in  the  year  one  thousand,  nine  hundred  and 

WHEREAS,  the  said   has  entered  into  a  con- 
tract with  the  said  for  the  building  of  conduits  for 

electrical  wires  in  the   City   of    in  the   State  of 

bearing  date  the  day  of  

one  thousand,  nine  hundred  and 

NOW,  THE  CONDITION  OF  THIS  OBLIGATION  IS  SUCH,  that  if 

the  said   shall  well  and  truly  keep  and  perform  all 

the  terms  and  conditions  of  the  said  contract  on  its  part  to  be  kept  and 

performed,  and  shall  indemnify  and  save  harmless  the  said  

as  herein  stipulated,  then  this  obligation  shall  be  of  no  effect;  otherwise 

it  shall  remain  in  full  force  and  virtue. 

(Witnesses)   (Signed)  , 


Construction  Costs. — The  cost  of  construction  and  of  materials 
varies  so  much  with  different  localities  that  it  is  impossible  to 
give  data  which  could  be  considered  standard  for  all  classes  of 
work;  and  the  following  schedule,  which  is  compiled  to  serve  as 
a  guide  in  making  up  estimates,  is  such  as  to  cover  average 
conditions.  The  figures  include  the  cost  of  all  materials,  excava- 
tion, removing  dirt,  mixing  and  placing  concrete,  hauling  and 
laying  duct,  replacing  pavement  and  the  expense  of  city  inspec- 
tion. In  the  conduit  cost,  the  figures  provide  for  the  duct  line 
to  be  surrounded  on  all  sides  by  a  3-in.  envelope  of  concrete,  the 
top  row  of  ducts  being  30  in.  beneath  the  surface. 

The  cost  of  removal  of  obstructions  is  an  item  which  cannot 
be  estimated  with  any  degree  of  certainty.  The  expense  of  this 
work  will  vary  from  5  to  50  cts.  per  ft.,  depending  on  the  size 
of  conduit  and  the  number  of  obstructions. 

Since  it  is  difficult  for  workmen  to  carry  on  the  work  in  a  trench 
less  that  18  in.  wide,  it  is  necessary  to  remove  a  strip  of  pavement 
of  at  least  this  width.  Engineering  expense  will  also  vary  con- 
siderably, depending  on  whether  the  work  involves  any  special 
features. 

Table  IV  gives  the  estimated  cost  of  single-tile  duct  under 
various  kinds  of  pavement,  and  a  similar  cost  for  fiber  conduit 
is  given  in  Table  V. 


CONDUIT  AND  MANHOLE  CONSTRUCTION 


77 


TABLE  IV. — SINGLE  TILE  DUCT  COSTS.    ESTIMATED  COST  PER  100  FT.  OP 

CONDUIT 

Based  on  3-in.  tile  duct,  3  in.  of  concrete  on  all  sides  and  top  of  conduit 
30  in.  below  the  grade  of  the  street 

Amounts 


Items 

Number  of  duct 

2 

4 

6 

9 

12 

16 

20 

Excavation  and  re- 
moval, cu.  yd  
Excavation  and  re- 
filling, cu.  yd  .  .    . 

4.12 

11.77 
200 
3.05 
184 

5.98 

11.77 
400 
3.78 
184 

7.85 

15.43 
600 
4.51 
217 

10.29 

15.43 
900 
5.25 
217 

12.73 

15.43 
1,200 
5.98 
217 

15.76 

19.10 
1,600 
6.92 
260 

18.78 

19.10 
2,000 
7.45 
260 

Duct,  ft 

Concrete,  cu.  yd  
Paving,  sq  ft 

Cost  of  conduits 


Excavation  and  re- 
moval, $1.00  per  cu. 
yd                       .    . 

$4  12 

$5  98 

$7  85 

$10  29 

$12  73 

$15  76 

$18  78 

Excavation  and  refill- 
ing, 60cts.  per  cu. 

yd 

7  06 

7  06 

9  26 

9  26 

9  26 

11  46 

11  46 

Duct,  6  cts.  per  ft. 
laid  

12.00 

24.00 

36.00 

54.00 

72.00 

96.00 

120.00 

Concrete,  $7.00  per 
cu.  yd  . 

21.35 

26.46 

31.57 

36.75 

41.86 

48  44 

52.15 

Plus  20  per  cent.1.  .  . 
Total  cost  :  .  . 

8.91 
53.44 

12.70 
76.20 

16.94 
101.62 

22.06 
132.36 

27.17 
163.02 

34.33 
205.99 

40.48 
242.87 

Cost  of  p.aving 


Macadam,  10  cts.  per 
sq.  ft  

$18.40 

$18.40 

$21.70 

$21.70 

$21.70 

$26  00 

$26  00 

Belgian  block  on 
sand,  15  cts.  per  sq. 
ft  

27.60 

27.60 

32  55 

32  55 

32.55 

39  00 

39  00 

Asphalt,  25  cts.  per 
sq  ft 

46  00 

46  00 

54  25 

54  25 

54  25 

65  00 

65  00 

Granite  block  and 
brick,  35  cts.  per  sq. 
ft 

64  40 

64  40 

75  95 

75  95 

75  95 

91  00 

91  00 

Wood  block,  37  cts. 
per  sq.  ft  

68.08 

68.08 

80.29 

£0.29 

80.29 

96.20 

96.20 

Total  cost  of  conduits 


Macadam  
Belgian     block     on 
sand 

$71.84 
81  04 

$94.60 
103  80 

$123.32 
134  17 

$154.06 
164  91 

$184.72 
195  57 

$231.99 
244  99 

$268.87 
281  87 

Asphalt 

99  44 

122  20 

155  87 

186  61 

217  27 

270  99 

302  87 

Granite    block    and 
brick     

117  84 

140  60 

177  57 

208  31 

238  97 

296  99 

333  87 

Wood  block  

121  52 

144.28 

181  91 

212  65 

243  31 

302  19 

339  07 

1  Covers  Engineering,  Inspection,  Sheathing,  Obstructions,  Insurance,  eto. 


78       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


TABLE  V. — FIBER  DUCT  COSTS.    ESTIMATED  COST  PER  100  FT.  OP  CONDUIT 

Based  on  3-in.   Fiber  Duct,  3  in.  of  Concrete   on  all  Sides  and  Top  of 

Conduit  30-in.  Below  the  Grade  of  the  Street 

Amounts 


Items 

Number  of  duct 

2 

4 

6 

9 

12 

16 

20 

Excavation  and  re- 
moval, cu.  yd  
Excavation  and  re- 
filling, cu.  yd  
Duct,  ft 

3.42 

10.80 
200 
2.93 
166 

5.04 

10.80 
400 
4.05 
166 

6.66 

14.27 
600 
5.19 
200 

8.80 

14.27 
900 
6.58 
200 

10.95 

14.27 
1,200 
7.99 
200 

13.61 

17.75 
1,600 
9.65 
250 

16.27 

17.75 
2,000 
11.33 
250 

Concrete,  cu.  yd  .... 
Paving,  sq.  f  t  

Cost  of  conduits 


Excavation  and  re- 
moval $1.00  per  cu. 

yd  
Excavation  and  re- 
filling, 60  cts.  per 
cu.  yd  

$     3.42 

6.48 
10.00 

20.51 
8.08 
48.49 

$     5.04 

6.48 
20.00 

28.35 
11.97 

71.84 

$     6.66 

8.56 
30.00 

36.33 
16.31 
97.86 

$     8.80 

8.56 
45.00 

46.06 
21.68 
130.10 

$  10.95 

8.56 
60.00 

55.93 
27.09 
162.53 

$  13.61 

10.65 
80.00 

67.55 
34.36 
206.17 

$  16.27 

10.65 
100.00 

79.31 
41.25 
247.48 

Duct,  5  cts.  per  ft. 
laid  

Concrete,  $7.00  per 
cu.  yd  
Plus  20  per  cent.1  .  .  . 
Total  cost  

Cost  of  paving 

Macadam,  10  cts.  per 
sq.  ft  
Belgian     block     on 
sand.  15  cts.  persq. 
ft.      . 

$  16.60 

24.99 
41.59 

58.19 
61.42 

$  16.60 

24.99 
41.59 

58.19 
61.42 

$  20.00 

30.00 
50.00 

70.00 
74.00 

$  20.00 

30.00 
50.00 

70.00 
74.00 

$  20.00 

30.00 
50.00 

70.00 
74.00 

$  25.00 

37.50 
62.50 

87.50 
92.50 

$  25.00 

37.50 
62.50 

87.50 
92.50 

Asphalt,  25  cts.  per 
sq  ft     .      . 

Granite   block    and 
brick    35    cts.    per 
sq.  ft 

Wood  block  37  cts. 
per  sq.  ft  

Total  cost  of  conduit 


Macadam  

$  64.09 

$  88  44 

$117.86 

$150.10 

$182.53 

$231  .  17 

$272.48 

Belgian     block     on 
sand 

73  44 

96  83 

127  86 

160  10 

192  53 

243  67 

284.98 

Asphalt.. 

90  08 

113  43 

147  86 

180  10 

212  53 

268  67 

309.98 

Granite    block    and 
brick.  ... 

106  68 

130  03 

167  86 

200  10 

232  53 

293.67 

334  .  98 

Wood  block  

109  91 

133  26 

171  86 

204  10 

236  53 

298.67 

339.98 

1  Covers  engineering,  inspection,  sheathing,  obstructions,  insurance,  etc. 


CONDUIT  AND  MANHOLE  CONSTRUCTION 


79 


As  these  tables  include  unit  quantities,  the  costs  may  be  revised 
to  suit  local  conditions  where  actual  unit  costs  are  known. 

As  in  the  case  of  conduit  construction,  the  cost  of  manholes 
also  varies  with  different  localities.  For  city  work,  and  especially 
in  congested  districts,  brick  is  sometimes  more  suitable  than 
other  forms.  Where  numerous  obstructions  are  met  with,  a 
manhole  made  of  brick  can  readily  be  made  of  such  shape  as  to 
avoid  other  structures.  In  cross-country  work  the  concrete  man- 
hole is  cheaper,  since  the  iron  or  wooden  forms  can  be  used  a 
number  of  times.  The  figures  given  in  Table  VI  and  Table  VII 
may  safely  be  used  for  estimating.  These  include  all  material 
and  labor  (exclusive  of  paving)  and  the  cost  of  the  cast-iron  frame 
and  cover. 

TABLE  VI. — BRICK  CONSTRUCTION 
Estimated  Costs  of  Manholes 


8  by  10  ft. 
by  6  ft. 
6  in. 

7  by  9  ft. 
by  6  ft. 
6  in. 

6  by  8  ft. 
by  6  ft. 
6  in. 

6  by  6  ft. 
by  6  ft. 
6  in. 

5  by  7  ft. 
by  6  ft. 
6  in. 

4  by  7  ft. 
by  6  ft. 
6  in. 

Excavation  and  removal  

$  37.00 

$  34.00 

$  30.00 

$  23.00 

$  21.00 

$  18.00 

Brick  in  place  

120.00 

110.00 

96.00 

86.00 

86.00 

L60.00 

Rail  

22.00 

18.00 

15.00 

14.00 

9.00 

f9.00 

Head  and  cover  

26.00 

26.00 

26.00 

26.00 

26.00 

26.00 

Concrete  

13.00 

12.00 

9.00 

7.00 

7.00 

7.00 

Incidentals  

20.00 

20.00 

18.00 

15.00 

15.00 

12.00 

Supervision 

5  00 

5  00 

5  00 

4  00 

4  00 

3  00 

$243.00 

$225.00 

$199.00 

$175.00 

$168.00 

$135.00 

TABLE  VII. — MONOLITHIC  CONCRETE  CONSTRUCTION 


8  by  10  ft. 
by  6  ft. 
6  in. 

7  by  9  ft. 
by  6  ft. 
6  in. 

6  by  8  ft. 
by  6  ft. 
6  in. 

6  by  6  ft. 
by  6  ft. 
6  in. 

5  by  7  ft. 
by  6  ft. 
6  in. 

4  by  7  ft. 
by  6  ft. 
6  in. 

Excavation  and  removal  

$37.00 
84  00 

$  34.00 
78  00 

$  30.00 
63  00 

$  23.00 
54  00 

$  21.00 
52  00 

$  18.00 
48  00 

Rail  -.  

22.00 

18.00 

15.00 

14.00 

9.00 

8  00 

Head  and  cover  

26.00 

26.00 

26.00 

26.00 

26  00 

26  00 

10  00 

10  00 

10  00 

8  00 

8  00 

7  00 

Incidentals  

18.00 

17.00 

14.00 

12.00 

12  00 

10  00 

Supervision  

5.00 

5.00 

5.00 

4  00 

4  00 

3  00 

$202.00 

$188.00 

$163.00 

$141.00 

$132.00 

$120.00 

The  above  estimated  costs  are  exclusive  of  paving. 

When  the  area  and  type  of  the  pavement  is  known,  the  cost 
can  be  estimated  and  added  to  the  figures  given  in  the  table 
to  obtain  a  total  cost. 


80       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


As  previously  stated,  under  certain  conditions  concrete  man- 
holes may  be  constructed  at  a  cost  somewhat  less  than  that  of 
brick  construction,  and  the  relation  between  the  cost  of  the  two 
forms  of  construction  is  shown  in  Fig.  37a.  This  curve  is  com- 


1.00 


20 


100 


200 


300 


400 


500 


Cubic  Feet 
FIG.  37 a. — Approximate  cost  of  manholes  exclusive  of  paving. 

puted  on  the  basis  of  the  cost  per  cubic  foot  of  manholes  of  various 
sizes. 

For  further  details  the  reader  is  referred  to  the  various  elec- 
trical handbooks  which  include  underground  construction  costs. 


CHAPTER  IV 


METHODS  OF  DISTRIBUTION 

Street  Distribution. — In  large  cities  the  arrangement  of  service 
laterals  and  subsidiary  connections  from  the  main  duct  line  to 
the  consumer's  premises  is  a  matter  of  importance  because  it 
forms  a  large  part  of  the  underground  investment.  A  single- 
conduit  system  with  service  connections  is  shown  in  Fig.  38. 
In  some  cases  it  is  advisable  to  install  duplicate  conduit  lines  in 
the  same  street;  one  conduit  consisting  of  a  sufficient  number  of 
ducts  to  carry  all  the  main  cables,  and  the  other  usually  consist- 
ing of  about  four  ducts  on  the  opposite  side  of  the  street  for  dis- 
tribution cables,  Fig.  39.  The  main  conduit  also  carries  about 


FIG.  38. — Service  handholes  and  laterals,  single-conduit  system, 


four  ducts  reserved  for  these  purposes.     In  Fig.  40  is  shown  a 
single-conduit  system  with  crossings. 

The  desirability  of  installing  duplicate  conduit  depends  en- 
tirely upon  local  conditions  and  the  width  of  the  street.  With 
duplicate-conduit  systems  the  service  or  lateral  connections  are 
usually  of  a  shorter  length  than  in  the  single-conduit  system  and 
the  service  holes  are  placed  about  100  ft.  apart.  Where  the 
streets  are  more  than  100  ft.  wide  a  double-conduit  line  installa- 
tion is  convenient  as  it  saves  long  lateral  connections.  In 
some  localities  a  single  service  connection  serves  several  buildings, 
the  intermediate  buildings  being  connected  by  means  of  interior 

6  81 


82       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


wiring  through  the  side  wall  or  basement.  While  this  method  is 
considerably  cheaper  than  supplying  individual  service  to  each 
building,  and  requires  fewer  distribution  holes,  it  has  the  dis- 
advantage that  a  fault  in  the  main  wiring  will  interrupt  service 
in  all  the  buildings  connected  thereto.  If  such  a  fault  develops 
in  the  service  connection  supplying  a  building  which  is  closed 


FIG.  39. — Service  handholes  and  laterals,  double-conduit  system. 

during  certain  hours  of  the  day  while  the  other  buildings  are 
still  open,  it  is  sometimes  difficult  to  gain  entrance  in  order  to 
make  necessary  repairs  and  to  restore  service  to  other  buildings 
tied  in  on  the  same  service.  Still  another  system  which  is  simi- 
lar to  the  duplicate  conduit  is  to  provide  crossings  at  each  dis- 


I    \     J 


Ml           1       M       1 

FIG.  40. — Service    handholes    and    laterals,    single-conduit    system    with 

crossings. 

tribution  hole  from  which  the  service  connections  are  run  on 
each  side  of  the  street. 

Interior  Block  Distribution. — What  is  commonly  known  as 
back-yard  or  block  system  of  distribution,  Fig.  41,  has  been  used 
quite  extensively  in  the  suburban  sections  of  a  number  of  large 


METHODS  OF  DISTRIBUTION 


83 


cities.  From  the  results  obtained  through  its  introduction 
there  seems  to  be  good  reason  for  the  enthusiastic  way  in  which 
it  has  been  taken  up.  So  far  as  appearances  go  this  plan  pos- 
sesses nearly  all  the  advantages  of  the  complete  duct  system  and 
the  cost  of  reaching  suburban  houses  with  electrical  service 
in  sections  where  the  underground  connections  in  streets  would 
be  necessitated,  is  not  much  greater  than  would  be  entailed  by 
the  straight  overhead  system.  In  the  larger  cities  arrangements 
have  been  made  whereby  the  lighting  companies  have  deeded 
to  them  by  the  owner  of  the  property  the  ground  on  which  poles 
may  be  erected  in  the  rear  of  houses,  together  with  the  right  of 


FIG.  41. — Plan  of  back-yard  pole  lines,  with  overhead-service  connection 
fed  from  main  subway. 

free  access  at  all  times,  the  company  in  return  for  this  privilege 
placing  on  the  street  an  improved  type  of  lamp  post.  In  this 
method  of  distribution  the  mains  are  run  to  the  back-yard  lines 
and  the  high-potential  circuits  are  run  underground  to  the  trans- 
former manhole  nearest  the  desired  streets.  From  this  point 
low-potential  circuits  run  to  the  street  opposite  the  pole  line 
whence  they  branch  and  run  underground  to  the  end  pole  on  the 
other  side.  The  mains  are  then  brought  up  through  conduits 
to  the  crossarm.  Service  connections  are  made  to  the  main  and 
brought  in  to  the  rear  of  the  house,  thus  relieving  the  front  of  the 
property  from  overhead  wires  and  service  connections.  The 
pole  line  extends  from  block  to  block,  depending  on  the  number  of 


84       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

houses  to  be  connected.  The  property  owner  usually  appreciates 
the 'effort  to  keep  the  streets  free  from  poles  and  the  shade  trees 
from  being  killed  or  marred  owing  to  the  presence  of  overhead 
wires  in  the  street.  Few  difficulties,  therefore,  are  encountered 
in  securing  free  grant  of  the  ground  and  the  right  of  access. 

The  scheme  has  met  with  public  approval  in  many  cities  where 
detached  houses  abound.  With  this  system  of  distribution  the 
problem  of  street  lighting  becomes  more  difficult  as  it  involves  the 
use  of  long  overhead  branches  to  each  lamp,  or  underground 
laterals  of  the  same  length  at  a  considerably  greater  cost. 

The  need  of  a  cheap,  yet  good  system,  of  subway  distribution 
in  suburban  districts  is  being  felt  at  this  time  when  there  is  so 
much  agitation  about  the  injurious  effects  of  wires  in  trees.  The 
springing  up  of  shade  tree  commissions  in  the  larger  cities  has 
particularly  aggravated  the  situation.  It  is  believed  that  in 
sections  where  the  business  would  not  warrant  a  complete  installa- 
tion of  an  underground  system  the  combination  of  an  under- 
ground system  with  the  overhead  system  just  described  will  be 
most  satisfactory  and  economical. 

Sidewalk  Distribution. — In  the  sidewalk  system  of  distribu- 
tion the  conduit  is  usually  laid  under  the  grass  plot  between  the 
curb  and  the  sidewalk  with  han dholes  located  at  every  second 
property  line  from  which  the  service  pipes  lead  in  to  the  meter 
board  on  the  consumer's  premises.  Sometimes  the  ducts  are 
sunk  below  the  sidewalk  level,  the  record  of  their  exact  location 
being  kept  so  that  they  may  be  quickly  located  in  case  of  trouble. 
The  box  as  shown  in  Fig.  42  is  well  adapted  to  this  type  of  con- 
struction. It  is  constructed  of  cast  iron  with  a  removable  cover 
and  is  cast  with  holes  of  a  convenient  size  to  receive  the  duct 
and  the  service  pipe. 

Handholes  may  also  be  installed  with  a  cast-iron  cover  which 
is  set  flush  with  the  sidewalk.  Fig.  42  illustrates  an  installation 
of  this  type. 

The  duct  may  be  either  fiber  or  iron  pipe,  the  fiber  duct,  how- 
ever, being  considerably  cheaper  than  the  iron  pipe.  It  is  not 
necessary  to  lay  the  duct  in  concrete,  as  a  special  sleeve  may  be 
employed,  which  has  sufficient  strength  to  insure  proper  align- 
ment of  the  duct  during  the  refilling  of  the  earth.  The  ends  of 
the  duct  should  fit  tightly  in  the  sleeve,  which  is  about  5  in.  long. 
Cement  covered  joints  are  also  used  to  good  advantage  when  the 
conduit  is  not  entirely  laid  in  concrete.  In  this  case  slip  joints 


METHODS  OF  DISTRIBUTION 


85 


are  wrapped  with  muslin  tape  before  the  protective  covering  of 
cement  is  applied,  thus  preventing  any  water  from  entering  the 
conduit.  This  system,  however,  has  its  limitations  and  is 
practicable  only  in  suburban  sections  where  the  houses  set  well 
back  from  the  property  line  and  have  no  vaults  extending  to  the 
curb. 

In  the  larger  cities  where  real  estate  promoters  have  built 
blocks  of  houses,  and  desire  to  keep  all  overhead  wires  off  the 
property,  it  is  customary  for  them  to  install  subway  services  to 
the  sidewalk  distribution  system,  since  the  revenue  from  the 


FIG.  42. — Sidewalk  distribution. 

customers  is  very  often  not  sufficiently  large  to  justify  the  ex- 
penditure on  the  part  of  the  lighting  company  of  the  amount 
necessary  to  install  underground  connections.  An  agreement 
with  the  owner  is  made  whereby  the  latter  will  install  the  conduit 
at  his  own  expense  under  the  supervision  of  the  company,  the 
company  agreeing  to  install  the  necessary  wiring  without  any 
future  expense  to  the  owner. 

Duct  Arrangement. — Conduit  lines  of  a  large  number  of  ducts 
are  undesirable  and  should  be  avoided  wherever  possible.  More 
than  20  or  24  cables  entering  a  manhole  by  one  conduit  line  are 
difficult  to  properly  train  around  the  manhole  walls  and  a  man- 


86       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

hole  fire  with  so  many  exposed  cables  may  cause  great  trouble 
and  damage. 

Unless  conditions  are  such  as  to  make  it  absolutely  necessary, 
it  is  not  good  practice  to  use  more  than  20  ducts,  partly  because 
of  the  limiting  of  the  current-carrying  capacity,  due  to  the  diffi- 
culty in  dissipating  the  heat  from  the  line  and  partly  because 
of  the  danger  of  shutting  down  the  whole  duct  line  due  to 
communication  of  trouble  from  one  cable  to  another. 

The  layout  of  the  conduit  system  should  be  one  which  will 
give  the  shortest  cable  lengths  and  at  the  same  time  avoid 
the  bunching  of  cables  in  any  one  manhole  or  conduit  run.  It 
is  advisable  to  divide  into  two  or  more  runs  at  the  supply  point 
or  center  of  distribution,  such  as  the  generating  station  or  sub- 
station. When  the  number  of  cables  for  present  and  future  use 
has  been  ascertained,  the  various  duct  sections  to  be  laid  should 
be  determined  by  increasing  the  number  of  ducts  required  by 
25  or  30  per  cent. 

This  increase  is  advisable  on  account  of  the  relative  cheapness 
of  the  ducts  so  installed  as  compared  with  the  high  cost  of 
installing  needed  ducts  at  some  future  time  when  unforeseen 
contingencies  require  their  use. 

While  the  number  of  ducts  will  be  fixed  by  requirements,  there 
must  be  sufficient  to  care  for  local  distribution  and  distribution 
feeders  and  transmission  lines,  as  well  as  to  care  for  future 
requirements. 

It  is  not  advisable  to  lay  less  than  four  ducts  in  a  line  except 
in  side  streets  or  for  lateral  connections  and  where  there  is  no 
probability  of  the  line  becoming  part  of  a  through  line. 

In  selecting  a  route  for  conduits,  due  consideration  should  be 
given  to  the  character  of  the  streets  or  alleys  in  which  the  work 
is  to  be  done.  It  often  develops  that  it  is  cheaper  to  lengthen 
the  conduit  and  cables  to  some  extent  than  to  install  them  in 
streets  where  very  expensive  pavement  is  laid  or  where  rock 
excavation  or  difficult  obstructions  will  be  encountered. 

Parallel  Routing. — Because  of  the  likelihood  of  large  cables 
in  one  conduit  or  in  one  street  to  be  interrupted  by  accidents,  the 
attempt  is  usually  made,  in  case  of  important  lines  running  from 
a  power  house  for  some  distance,  to  route  them  in  separate  con- 
duit lines  or  even  in  separate  streets,  and  it  is,  therefore,  advisable, 
instead  of  using  a  large  number  of  ducts,  to  provide  parallel 
conduit  lines  with  fewer  ducts.  Among  some  of  the  causes 


METHODS  OF  DISTRIBUTION 


87 


which  might  interrupt  such  lines  are  burning  of  cables  by  severe 
short-circuits,  by  caving  in  of  streets  due  to  excavation  for 
building  foundations,  sewers  or  subway  construction,  explosions 
due  to  illuminating  gases,  blasting,  malicious  mischief,  washing 
out  of  pavement  and  conduit  due  to  bursting  of  water  mains, 
collapse  of  large  buildings  in  case  of  fires,  earthquakes  or  faulty 
construction. 

In  Fig.  43  is  shown  a  system  with  all  main  cables  installed  in 
a  single-conduit  system. 


Sue  STATIO/V 


FIG.  43. — Feeder  cables  routed  in  same  duct  lines. 

While  much  of  this  constitutes  an  ever-present  menace,  any 
real  danger  of  interruption  of  service  on  any  line  from  these  causes 
is  quite  remote  and  the  justification  of  any  increased  investment 
to  provide  a  duplicate  route  should  be  gaged  accordingly.  Some 
engineers  are  of  the  opinion  that  the  greatest  protection  warrant- 
able would  be  to  provide  duplicate  routes  for  conduit  lines  in  the 
same  streets.  Others  go  to  the  extreme  of  providing  a  duplicate 
route  for  a  single  line,  which  necessitates  a  much  longer  run  than 
the  original  route. 

Inquiries  among  a  number  of  the  leading  companies  show  that 
some  would  not  provide  a  duplicate  if  it  required  any  material 


88       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

increase  in  the  length  of  the  second  line,  while  others  in  some 
special  cases  would  favor  the  use  of  a  duplicate  route,  as  shown 
in  Fig.  44. 

In  order  to  avoid  more  than  two  cables  paralleling  along  the 
wall  of  the  manhole  at  the  same  elevation,  the  conduit  should  be 
so  arranged  that  not  more  than  four  ducts  in  width  enter  a  man- 
hole. Where  the  conduit  is  several  ducts  wide,  it  is  frequently 
found  advantageous  to  separate  the  ducts  where  they  enter  the 
manhole.  The  arrangement  of  the  ducts,  however,  is  usually 
determined  by  the  space  available  in  theL  street. 


FIG.  44. — Feeder  cables  routed  in  different  duct  lines. 

Where  conditions  will  allow,  a  good  form  of  duct  arrangement 
is  as  follows: 

Two-,  four-  and  six-duct  conduit Two  ducts   wide. 

Nine-  and  twelve-duct  conduit Three  ducts  wide. 

Sixteen-,   twenty-    and    twenty-four-duct 

conduit Four  ducts  wide. 

Solid  System. — The  need  for  an  inexpensive  system  of  under- 
ground distribution  in  suburban  sections  where  the  complete 
installation  of  a  drawing-in  system  would  be  prohibitive  on  ac- 
count of  the  cost,  has  led  some  companies  to  experiment  with 


METHODS  OF  DISTRIBUTION 


89 


a  so-called  "solid"  system.  One  of  the  large  illuminating  com- 
panies several  years  ago  constructed  a  system  which  consisted 
of  fiber  conduit  laid  directly  in  the  ground  without  concrete, 
but  with  a  protective  covering  of  "kyanized"  planking  resting 
directly  on  the  fiber  tube. 

The   conductors   consisted   of  ordinary  line   wire   and   were 
arranged  for  three-wire  distribution  with  the  center  or  neutral 


2  Plank 


2  Plank 


Compound 


Compound 


Fibre  Conduit ' 
Omitted  here 
to  show  Jointing 


INTERIOR  VIEW  OF  BOX 
SHOWING  SERVICE  CONNECTION 


SECTION  OF 
FIBRE  PIPE 

FIG.  45. — Experimental  solid  system. 

wire  lying  directly  in  the  earth  between  the   two   outside   con- 
ductors. 

After  laying  the  wire  the  fiber  tubes  were  filled  with  an  insulat- 
ing compound.  A  complete  installation  of  this  type  is  shown  in 
Fig.  45.  Service  connections  for  customers  were  made  by  remov- 
ing a  short  section  of  the  covering  and  connecting  service  wires 
to  the  mains,  after  which  the  joint  was  filled  with  compound  and 


90       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

the  covering  restored.  The  writer  has  been  advised  that  this 
system  has  been  in  service  for  about  8  years  in  suburban  sections, 
without  showing  any  indication  of  deterioration,  and  with  no 
displacement  of  the  compound  during  the  summer  months  even 
when  laid  on  5  per  cent,  grades. 

The  compound  used  in  the  installation  shows  a  dielectric 
strength  of  about  2,300  volts  per  in.  and  an  expansion  from  solid 
to  liquid  from  5  to  10  per  cent.  It  is  not  affected  by  moisture 
and  has  a  flash  test  of  about  700°F. 

Service  Connections. — Service  or  lateral  connections  from  man- 
holes to  the  consumers'  premises  are  usually  installed  in  wrought- 
iron  or  steel  pipe.  The  pipe  should  be  thoroughly  coated  with 
an  asphaltic  compound  or  other  suitable  protection  to  prevent 
corrosion.  Galvanized  or  sherardized  pipe  is  sometimes  used 
in  order  to  prolong  the  life  of  the  service.  In  a  number  of 
installations  the  iron  pipe  is  used  only  in  the  street  between  the 
manhole  and  the  curb  line  where  the  traffic  is  heavy,  and  under 
the  sidewalk  or  on  private  property  fiber  pipe  or  some  other  form 
of  conduit  may  be  used.  It  is  customary  in  installing  service 
connections  in  a  street  which  is  about  to  be  improved  with  a 
permanent  pavement,  to  install  the  laterals  not  only  to  present 
consumers,  but  also  to  prospective  customers,  terminating  the 
pipe  at  the  curb,  a  record  being  taken  of  the  exact  location  in 
order  that  the  service  may  be  continued  to  the  consumers, 
premises  as  the  occasion  requires. 

For  convenience  in  locating  the  pipe  services,  markers  are  fre- 
quently placed  in  the  sidewalk  to  fix  the  location. 

These  service  markers  consist  of  an  iron  rod  which  is  driven 
into  the  ground  to  the  end  of  the  pipe.  The  rod  is  capped  with 
a  cast-iron  plate  which  indicates  the  class  of  service. 

Wooden  plugs  or  metal  caps  are  placed  at  the  end  of  the  pipe 
in  order  to  prevent  earth  or  other  material  entering  the  pipe 
when  the  excavation  is  being  refilled. 

It  is  frequently  found  necessary  to  install  service  pipes  under 
cement  sidewalks  or  under  highways,  and  since  such  installations 
require,  a  permit  and  the  expenditure  of  considerable  money 
for  restoration  of  the  pavement,  the  use  of  a  pipe-forcing  jack 
will  be  found  economical.  This  jack  is  specially  designed  for 
forcing  pipe  horizontally  through  the  ground  and  may  be  used 
advantageously  where  it  is  desired  to  install  pipe  under  the  con- 
ditions mentioned  above,  or  under  railroad  tracks  or  other  cross- 


METHODS  OF  DISTRIBUTION  91 

ings.  The  device  effects  a  considerable  saving  in  both  time  and 
money.  This  jack,  which  is  illustrated  in  Fig.  46  consists  of  a 
carriage  which  travels  on  a  track  so  designed  that  when  the 
carriage  reaches  the  limit  of  its  travel  it  can  be  drawn  back  to 
the  starting  point  to  permit  of  a  new  section  of  pipe  being  in- 
serted. The  operation  of  this  apparatus  is  thus  carried  on 
until  the  desired  distance  to  which  the  pipe  is  to  be  forced  has 
been  reached.  It  has  been  found  advisable  to  provide  for  the 
driving  in  of  a  section  of  pipe  1  or  2  ft.  long  and  of  a  size  larger 
than  the  pipe  to  be  laid.  .  This  short  length  of  pipe  is  equipped 


FIG.  46. — Pipe  forcing  jack  showing  pipe  and  steel  nose  mounted  in  position. 

with  a  steel  nose  so  that  it  can  readily  cut  its  way^through  a 
reasonable  amount  of  earth,  rock  and  stones  or  roots  in  its  path. 
Under  favorable  soil  conditions  this  jack  will  force  pipe  up  to 
4  in.  in  diameter  for  a  reasonable  distance.  In  using  the  jack 
in  public  highways,  however,  care  should  be  taken  to  avoid  coming 
into  contact  with  any  foreign  structures,  as  the  writer  has  known 
of  several  cases  where  lack  of  care  has  caused  damage  to  under- 
ground pipes  or  other  conduits.  The  jack  should,  therefore,  be 
used  only  where  the  operator  is  certain  that  no  obstructions  of 
this  nature  will  be  encountered  in  the  path  of  the  pipe  being  forced. 
Underground  construction,  when  employed  for  service  con- 
nections of  small  capacity,  usually  requires  an  abnormal  invest- 


92       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

ment  in  comparison  with  the  business  to  be  served.  Where  a 
number  of  customers  in  a  single  building  are  to  be  served  by  a 
single  service,  local  municipal  regulations  usually  require  that 
the  main  service  switch  be  placed  in  a  location  accessible  at  all 
times  for  the  replacement  of  fuses,  etc. 

This  is  usually  easily  accomplished  in  a  building  one  or  more 
stories  in  height,  where  there  are  no  partitions  or  dividing  walls 
cutting  the  building  vertically  into  several  parts  by  locating 
the  service  in  the  main  entrance  or  in  some  position  in  the  base- 
ment which  is  used  in  common  by  all  tenants. 

In  the  case  of  a  block  of  one-story  buildings,  as  shown 
in  Fig.  47  constructed  with  or  without  basements,  each  having 


FIG.  47. — Method  of  installing  service  box  in  buildings. 

its  own  entrance,  recourse  must  be  had  to  installing  a  separate 
service  connection  to  each  subdivision  of  the  block,  as  shown  in 
Fig.  48. 

In  many  cases  such  services  may  serve  a  load  of  only  %  kw. 
or  even  less,  thus  involving  a  heavy  and  unwarranted  expenditure 
for  the  business  served. 

In  efforts  to  reduce  the  cost  of  this  form  of  construction,  a 
material  saving  has  been  effected  by  the  introduction  of  a  service 
box  adapted  for  the  supply  of  an  entire  block  or  group  of  cus- 
tomers of  the  character  last  described. 

The  service  box  comprises  a  suitable  weatherproof  iron  box 
built  into  the  wall  of  the  building  at  the  street  level  in  a  manner 
to  conform  to  the  general  architecture  of  the  building  and  in  no 
way  to  detract  from  its  appearance.  The  company  terminates 


METHODS  OF  DISTRIBUTION 


93 


its  service  in  this  box,  installing  a  main  switch  properly  fused 
for  the  supply  of  the  entire  premises  to  be  served.  The  owner  of 
the  building  installs  a  common  main  from  the  service  box,  run- 
ning the  same  horizontally  to  connect  with  all  the  separate 
premises  to  be  served. 

This  main,  when  installed  in  conduit,  in  strict   accordance 
with  the  rules  of  the  National  Board  of  Fire  Underwriters,  intro- 


Manhole 


BLUE     HILL          AVE. 


Manhole 


Handholes 


-?* 

A 


Bowling  Alley 


Manhole 


COMMONWEALTH        AVE. 


FIG.  48. — Method  of  installing  separate  underground  services. 

duces  no  hazard  of  any  character,  and  simply  duplicates  the 
conditions  under  which  vertical  mains  or  risers  are  installed  to 
serve  tenants  in  buildings  of  one  or  more  stories  in  height.  In 
both  cases  branch  connections  are  taken  from  the  main  on  each 
tenant's  premises,  thus  giving  the  tenant  access  at  all  times  to  the 
devices  controllingjhis  service. 


94       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

The  main  service  box,  located  in  the  outside  wall  of  the  building, 
is  always  accessible  to  the  company's  employees  for  re-fusing, 
inspection,  etc.,  and  also  to  firemen  or  other  municipal  agents  who 
might  desire  to  discontinue  the  service  in  the  building  in  emer- 
gencies. While  the  box  is  ordinarily  locked,  provision  is  made 
for  forcing  the  door  without  damage  to  the  box  itself. 

Armored-cable  System. — In  Europe  the  installation  of  armored 
cable  is  practically  standard  for  all  underground  systems 
supplying  large,  as  well  as  small,  service  requirements. 

These  systems  employ  armored  cables  with  or  without  lead 
sheaths,  laid  directly  in  the  ground  or  in  insulated  troughs 
which  are  sometimes  filled  with  compound  as  may  best  suit  the 
local  conditions  governing  the  installation. 

Junction  or  distribution  boxes  are  employed  at  the  center 
of  distribution  and  service  connections  for  customers  are  made 
by  means  of  wiped  joints  where  lead-sheath  cables  are  employed 
and  by  connection  boxes  where  non-leaded  cables  are  used. 

In  the  latter  case  these  connection  points  are  filled  with  com- 
pound after  the  connection  is  completed.  In  this  country  the 
armored-cable  system  has  demonstrated  its  advantages  for  use 
in  cities  where  service  requirements  are  of  a  difficult  nature  and 
are  subject  to  radical  changes,  and  for  residence  streets  where 
there  is  a  strip  of  land  between  the  curb  and  the  sidewalk  line. 

It  can  readily  be  installed  in  places  where  the  dra wing-in 
system  would  be  impossible  owing  to  the  necessity  of  passing 
around  large  obstacles  such  as  rocks,  trees,  etc. 

The  necessity  for  a  safe  and  inexpensive  conduit  system  in 
many  of  the  smaller  cities  or  towns,  and  in  the  parks,  playgrounds 
and  boulevards  of  larger  cities,  has  brought  about  a  great  demand 
for  steel-tape  cable.  This  cable  is  made  in  various  sizes  and  is 
adapted  for  any  voltage.  The  conductors  are  insulated  with  a 
rubber  compound  and  taped.  After  the  required  number  of 
conductors  has  been  laid  and  covered  with  jute  and  tape,  a 
lead  sheath  is  applied  and  the  whole  served  with  jute.  The 
armor  is  then  applied.  This  usually  consists  of  two  layers  of 
steel  tape  over  which  is  applied  the  asphalt  and  jute  which 
serves  for  the  outside  or  final  layer,  as  illustrated  in  Fig.  49. 

Such  construction  is  closely  analogous  to  that  of  the  standard 
submarine  cable  and  each  layer  or  cover  has  its  special  function. 
The  outer  jute  covering  protects  the  steel  armor  against  the  ac- 
tion of  water  and  chemicals  and  the  steel  tape  affords  mechanical 


METHODS  OF  DISTRIBUTION 


95 


strength  and  protection  to  the  conductors.  The  layer  of  jute 
under  the  armor  acts  as  a  cushion  between  the  armor  and  the 
lead  sheath.  The  lead  sheath  absolutely  excludes  moisture. 
The  economies  effected  by  this  type  of  installation  have  allowed 
a  number  of  municipalities  to  install  street-lighting  systems  at  a 
minimum  cost.  The  growing  demand  for  improved  methods  in 
the  installation  of  ornamental  street-lighting  systems  using  under- 
ground conductors  seems  to  have  been  met  by  the  use  of  steel- 
armored  cable,  as  it  permits  the  installation  of  a  complete  system 


FIG.  49. — Forms  of  steel  taped  cable. 

in  the  minimum  time  and  at  the  least  cost,  in  any  kind  of  weather 
and  with  practically  no  interruptions  to  traffic. 

One  of  the  largest  installations  of  this  type  is  in  Central  Park, 
New  York  City,  where  over  500,000  ft.  of  steel-tape  street- 
lighting  cable  is  in  use. 

Installations  of  steel-armored  cables  have  been  in  service  in 
this  country  for  a  number  of  years  and  have  operated  very 
satisfactorily.  The  cable  is  usually  laid  about  1  ft.  deep  in  a 
trench  of  spade  width,  as  illustrated  in  Fig.  50.  No  reinforce- 
ment or  protection  is  provided  except  at  street  crossings  and 


96       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

roadways  where  there  is  apt  to  be  heavy  traffic.  At  such  places 
it  is  customary  to  run  the  cable  through  an  iron  pipe. 

Where  the  ground  is  sufficiently  level  the  cable  may  be  laid 
directly  from  the  reel  mounted  on  a  pair  of  wheels.  Where  neces- 
sary the  same  cables  may  be  used  as  submarine  cable  for  crossing 
lakes  or  streams.  No  joints  are  made  in  the  cable  as  it  is  usually 
looped  in  through  the  lamp  post.  Terminal  blocks  are  located 
in  the  bases  of  the  posts  as  shown  in  Fig.  51. 

Steel-tape  cable,  being  frostproof  and  waterproof,  may  be  laid 
just  deep  enough  to  prevent  accidental  damage  or  injury. 


FIG.  50. — Installation  of  armored  cable. 

Cable  has  been  used  to  good  advantage  where  it  has  been  found 
necessary  to  cross  railroad  tracks,  in  which  case  the  above  type 
of  installation  furnishes  an  ideal  solution  of  the  problem.  When 
crossing  under  tracks,  excavation  is  sometimes  avoided  entirely 
by  boring  through  the  ground  with  an  auger  and  slipping  the 
cable  through  the  hole  thus  made. 

The  writer's  investigation  regarding  the  experience  of  a  number 
of  companies  using  this  type  of  cable  indicates  that  troubles 
which  have  developed  have  been  due  chiefly  to  mechanical 
injury  to  the  system  caused  by  carelessness  or  accidents. 


METHODS  OF  DISTRIBUTION 


97 


If,  therefore,  the  cable  is  carefully  manufactured  and  properly 
installed,  it  is  rarely  necessary  to  take  it  up  again  to  locate  and 
repair  faults. 


3  WIRE  BLOCK 


CONTROL  SWITCH 
Neutral  Solid        Uo  Switch 

FIG.  51. — Terminal  blocks. 


Installing  Steel-taped  Street-lighting  Cable. — When  used  for 
ornamental  street  lighting,  the  usual  practice  is  to  bury  the  cable 
in  the  street  close  to  the  curb  and  just  beneath  the  paving. 
Where  the  street  is  paved  with  brick,  cobbles,  granite  or  wood 


98       UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

blocks,  the  installation  simply  requires  the  removal  of  one  or  two 
rows  of  the  paving  material  and  the  cable  is  laid  3  in.  below  the 
pavement,  filled  over  with  sand  and  the  paving  replaced. 

Another  method  largely  used  is  to  remove  one  course  of  brick 
or  block  next  to  the  curb,  lay  the  cable  in  and  cover  with  concrete 
to  the  pavement  level.  This  method  may  also  be  used  with 
asphalt  or  macadam  pavements,  a  shallow  groove  being  chopped 
or  chiseled  away,  the  cable  laid  in,  and  the  groove  filled  flush  with 
concrete.  In  either  of  these  cases,  the  cable  is  brought  up  to  the 
lighting  post  either  under  the  curbing  or  through  it,  and  up 
through  a  hole  in  the  sidewalk. 

Another  style  of  construction  sometimes  used  in  business 
districts  where  the  sidewalks  run  out  to  the  curb,  is  to  cut  a 
channel  in  the  walk  just  inside  the  curb  (about  2  in.  by  2  in.  in 
section)  in  which  the  cable  is  buried  in  concrete. 

Where  there  is  a  parkway  between  the  sidewalk  and  curb, 
the  cable  can  be  laid  in  a  narrow,  shallow  trench,  dug  in  the  sod 
inside  the  curb.  Where  an  intersecting  walk  is  encountered, 
it  can  be  crossed  in  a  narrow  channel  chiseled  out  and  filled  with 
concrete. 

When  crossing  intersecting  streets,  a  row  of  brick  or  block 
is  removed  and  the  cable  laid  beneath;  or  the  asphalt  or  macadam 
is  channeled,  the  cable  laid  in,  and  the  surface  restored.  If  car 
tracks  must  be  crossed,  a  hole  is  bored  beneath  the  track  and  the 
cable  pulled  through.  The  right-of-way  is  not  disturbed  and 
the  car  service  need  not  be  interrupted. 

Where  obstructions  of  any  kind  are  encountered  in  the  trench, 
the  cable  is  simply  pulled  under,  or  laid  around  the  obstacle. 

Where  the  standards  can  be  set  upon  concrete  walks  of  suffi- 
cient thickness  and  sound  quality,  no  other  footing  is  necessary. 
The  base  can  be  set  on  the  walk,  holes  marked  and  drilled,  and 
the  foundation  bolts  set  in  head  down,  bedded  in  lead,  sulphur 
or  grout.  A  hole  for  the  cable  is  drilled  through  the  walk,  and 
another  through  or  under  the  curb.  The  cable  is  brought  up 
through,  the  standard  set  over  it  and  bolted  in  place. 

When  there  is  no  cement  walk,  or  where  the  concrete  is  not 
strong  enough,  it  will  be  necessary  to  build  a  concrete  base  or  put 
in  a  cast-iron  sub-base  for  the  lamp  standard.  Fig.  52  shows  a 
simple  form  of  concrete  base  made  in  a  plain  square  wood  form. 

Instead  of  the  curved  tile  shown,  a  wood  box  may  be  used,  or 
a  piece  of  steel  conduit  or  iron  pipe.  In  some  cases  the  cable  has 
been  bedded  directly  in  the  green  concrete  base. 


METHODS  OF  DISTRIBUTION 


99 


It  is  advisable  to  connect  the  conductors  of  the  cable  to  a  cut- 
out in  the  base  of  the  lamp  standard,  at  least  a  foot  above  ground. 
The  jute  is  cut  away,  the  steel  tape  rolled  back  the  right  distance 
and  cut  off,  and  the  lead  casing  removed  to  within  about  1  in. 
of  the  end  of  the  steel  tape.  The  copper  conductors  are  then 
separated,  bared,  and  fitted  or  bent  into  loops  at  the  end,  for 
connection  to  the  cutout.  The  end  of  the  lead  sheath  should  be 
carefully  taped  and  painted  with  waterproof  compound,  to  seal 
it  against  moisture.  The  steel  tape  should  be  bound  with  wire 


FIG.  52. — Design  for  concrete  base  for  lamp  standard. 

at  the  end  and  the  outside  woven  covering  taped  or  wrapped  with 
twine  to  prevent  fraying. 

At  the  point  where  the  cable  connects  with  overhead  lines,  the 
best  practice  is  to  carry  the  cable  to  the  top  of  the  pole  and  make 
connection  in  a  suitable  pothead  for  protection  against  weather. 

In  an  installation  of  steel-taped  cable  for  ornamental  street 
lighting  at  Maryville,  Mo.,  74  five-light  standards  are  used,  the 
top  light  being  a  100-watt  Mazda  and  the  four  lower  lights 
being  40-watt  Mazdas.  The  top  light  burns  all  night,  and  the 
others  up  to  11:00  p.  m.  Three- wire  cable  is  used,  being  placed 
under  the  brick  pavement  at  the  curb. 


100     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


TABLE  VIII.— STEEL  TAPED  CABLE 
Dimensions   and   Weights 

600  Volts 


Single  conductor 

Two-conductor  flat 

Three-conductor 

Size  of  conductors 

ness  of 
rubber, 
in. 

Outside 
diame- 
ter, in. 

Approx. 
shipping 
weight  per 
M  ft.,  Ib. 

Outside 
diameter, 
in. 

Approx. 
shipping 
weight 
per  M  ft., 
Ib. 

Outside 
diameter, 
in. 

Approx. 
shipping 
weight 
per  M  ft., 
Ib. 

Solid 

12  B    &  S 

Ha 

0  687 

850 

0  970 

1  375 

1  030 

1  750 

10  B    &  S 

He 

0  720 

1,200 

1  000 

1  545 

1  062 

1  900 

8  B    &  S 

He 

0  750 

1  300 

1  062 

1  700 

1   125 

2  100 

6B.  &S  

He 

0.782 

1,365 

1.125 

2,045 

1.187 

2,500 

Stranded 

4B.  &S  

He 

0.875 

1,700 

1.312 

2,185 

1.375 

3,430 

2B.  &S  

He 

0.906 

1,875 

1.437 

2,810 

1.500 

4,010 

1  B.  &S  

& 

.000 

2,065 

1.625 

3,320 

1.687 

5,120 

OB.  &S  

564 

.030 

2,200 

1.687 

3,650 

1.812 

5,650 

00  B.  &  S  

K* 

.062 

2,400 

1.750 

3,900 

1.906 

6,250 

000  B.  &S  

^ 

.125 

2,600 

1.875 

4,620 

2.030 

7,125 

0000  B.  &S  

^ 

.187 

2,850 

2.000 

5,145 

2.156 

8,950 

2,400  Volts 


Solid 

12  B    &  S 

442 

0.781 

1,415 

1.  188 

2,100 

1.281 

2,790 

10  B.  &  S  

TO& 

%* 

0.813 

1,500 

1.213 

2,265 

1.328 

3,070 

8B.  &S  

K* 

0.828 

1,550 

1.250 

2,365 

1.375 

3,165 

6  B    &  S 

%2 

0.859 

1,640 

1.313 

2,535 

1.453 

3,415 

Stranded 

4B.  &S  

*J2 

0.938 

1,865 

.469 

2,970 

1.609 

4,075 

2B.  &S  

^2 

1.015 

2,085 

.625 

3,700 

1.734 

5,250 

IB.  &S  

%2 

1.047 

2,200 

.688 

3,840 

1.828 

5,600 

OB.  &S  

Vn 

'  1.034 

2,360 

.781 

4,120 

1.921 

6,110 

00  B.  &  S  

K* 

1.140 

2,550 

.875 

4,575 

2.046 

6,825 

000  B.  &  S  

K2 

1.218 

2,765 

.969 

4,950 

2.156 

7,950 

0000  B.  &  S  

te* 

1.281 

3,500 

2.094 

6,140 

2.281 

8,800 

5,000  Volts 


8B.  &S.  solid... 

%2 

1.062 

1,680 

1.375 

2,680 

1.656 

3,920 

6  B.  &  S.  solid..  . 

%2 

1.094 

1,800 

1.500 

2,900 

1.719 

4,220 

4  B.  &  S.  stranded 

%2 

1.156 

2,075 

1.719 

3,685 

1.906 

5,430 

The  diagram  (Fig.  53)  shows  the  wiring  scheme.  Two  trans- 
formers and  two  primary  circuits  are  required.  Switches  at  the 
station  control  each  primary  circuit  and  by  this  means  constant 
load  is  carried  on  each  transformer.  The  usual  practice  in  a 
system  of  this  kind  is  to  control  the  lights  by  means  of  switches 
placed  at  some  convenient  point  on  the  secondary  lines. 


METHODS  OF  DISTRIBUTION  101 

Table  VIII  lists  the  standard  specifications  for  steel-taped  cable 
in  the  voltages  for  which  it  is  regularly  manufactured.  Special 
sizes  and  voltages  not  listed  may  be  obtained  when  required. 

Comparative  Costs  of  Installation. — It  is  impossible  to  state 
just  what  the  saving  realized  by  a  system  of  steel-taped  cable  will 
be  over  a  conduit  system,  without  a  careful  analysis  of  the  con- 
ditions. In  general  it  may  be  said  that  the  saving  will  rarely 
be  less  than  30  per  cent.,  and  may  run  higher,  under  conditions 


CUTOUT  1600!  CUTOUT 


/=>OST 


VWW  WvW 


^/VW\ 
A/»./ 


5 


FIG.  53. — Wiring  diagram  for  street  lamps. 

peculiarly  adverse  to  the  conduit.  In  fact,  the  cable  has  been 
successfully  and  cheaply  installed  under  conditions  which  abso- 
lutely prohibited  the  use  of  conduit. 

The  following  comparison  has  been  worked  out  on  some  arbi- 
trary assumptions,  with  a  special  effort  to  make  the  figures  just 
in  each  case.  A  length  of  1,000  ft.  is  taken  as  a  basis  of  compari- 
son, laid  in  brick-paved  streets: 

Cost  of  lead-encased,  600-V.R.C.  cable  in  fiber  duct: 

1,000  ft.  No.  6  three-conductor  cable $200 

1,000  ft.  2-in.  fiber  conduit 50 

Cost  of  installing  in  loop  system 420 


$670 
Cost  of  steel-taped,  600-V.R.C.  cable: 

1,000  ft.   No.   6  three-conductor,   600-volt  steel-taped 

cable $260 

Cost  of  installing  in  loop  system 165 


$425 
Saving  by  the  use  of  steel-tape  cable,  $245,  or  36  per  cent. 


CHAPTER  V 
CABLES 

General. — In  present-day  practice  of  underground  construction 
lead-covered  insulated  cables  are  used  almost  exclusively.  The 
three  essential  members  of  such  a  cable  are:  The  conductor  itself, 
the  wall  of  insulating  material  and  the  outer  protective  covering, 
and  they  will  be  considered  in  the  order  named. 

Terminology. — The  following  definitions  relating  to  wire  and 
cables  are  based  on  Bulletin  No.  37,  issued  by  the  Bureau  of 
Standards,  January,  1915. 

WIRES  AND  CABLES 

Wire. — A  slender  rod  or  filament  of  drawn  metal. 

Conductor. — A  wire,  a  combination  of  wires  not  insulated  from  one  an- 
other, suitable  for  carrying  a  single  electric  current. 

Stranded  Conductor. — A  conductor  composed  of  a  group  of  wires,  or  of 
any  combination  of  groups  of  wires. 

Cable. — (1)  A  stranded  conductor  (single-conductor  cable) ;  or  (2)  a  com- 
bination of  conductors  insulated  from  one  another  (multiple-conductor 
cable). 

Strand. — One  of  the  wires  or  groups  of  wires  of  any  stranded  conductor. 

Stranded  Wire. — A  group  of  small  wires  used  as  a  single  wire. 

Cord. — A  small  and  very  flexible  cable,  substantially  insulated  to  with- 
stand wear. 

Concentric  Strand. — A  strand  composed  of  a  central  cord  surrounded  by 
one  or  more  layers  of  helically  laid  wires  or  groups  of  wires. 

Duplex  Cable. — Two  insulated  conductor  cables,  twisted  together. 

Twin  Cable. — Two  insulated  single-conductor  cables,  laid  parallel,  hav- 
ing a  common  covering. 

Triplex  Cable. — Three  insulated,  single-conductor  cables  twisted  together. 

Twisted  Pair. — Two  small  insulated  conductors  twisted  together  without 
a  common  covering. 

Twin  Wire. — Two  small  insulated  conductors  laid  parallel,  having  a  com- 
mon covering. 

Conductor. — Theoretically  the  transmission  of  electricity 
through  any  substance  is  a  matter  of  degree;  practically  we  may 
make  a  distinction  between  conducting  and  insulating  materials. 

102 


CABLES  103 

The  following  table  gives  a  list  of  materials  approximately  ar- 
ranged in  order  of  their  conducting  powers. 

Conductors  Non-conductors  or  insulators 

All  metals Dry  air  Ebonite 

Well-burned  charcoal Shellac  Gutta  percha 

Plumbago Paraffine  India  rubber 

Acid  solutions Rosins  Silk 

Metallic  ores Sulphur  Dry  paper 

Living  vegetable  substances Wax  Dry  leather 

Moist  earth Glass  Porcelain 

Water Mica  Oils 

The  conducting  power  of  any  substance  depends  largely  upon 
its  physical  state,  and  the  conductivity  of  all  substances  materi- 
ally alters  with  a  change  of  temperature. 

The  general  trend  of  this  change  in  conductivity  with  rising 
temperature  is  toward  a  decrease  with  metals  and  toward  an 
increase  with  other  substances. 

In  commercial  transmission  of  electricity  we  are  limited  to 
the  use  of  three  metals:  copper,  iron  and  aluminum,  although 
abnormal  conditions  of  late  have  added  zinc  in  certain  countries. 
Copper  ranks  first  in  importance,  with  aluminum  next,  and  iron 
last,  and  whether  or  not  the  use  of  zinc  will  survive  after  normal 
conditions  are  restored  appears  uncertain.  Pure  copper,  in 
addition  to  its  high  conductivity,  possesses  many  other  physical 
properties  of  special  value  in  cable  work. 

Its  strength,  malleability  and  cost  in  comparison  with  that  of 
other  metals  makes  it  an  ideal  material  for  cable  work.  The 
malleability,  ductility,  tensile  strength  and  electrical  conduc- 
tivity of  copper  are  somewhat  modified  by  impurities.  These, 
when  present,  usually  are  of  one  or  more  elements  such  as  bis- 
muth, arsenic,  antimony,  sulphur,  etc.;  however,  the  electrolytic 
wire  bars  so  largely  used  in  the  manufacture  of  wires  and  cables 
for  electrical  purposes  are  almost  pure. 

Refining  of  copper  and  its  separation  from  the  multitude  of 
alloying  metals  is  a  complex  metallurgical  process,  but  a  very 
necessary  one.  Even  traces  of  other  metals  affect  the  con- 
ductivity to  a  remarkable  degree,  as  the  following  table  will 
show: 


104     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

Element  ^er  cen*-  present         Per  cent,  con- 

in  copper  ductivity 

Carbon 0.05  77.87 

Sulphur 0.18  92.08 

Arsenic 0 . 10  73 .89 

Silver 1.22  90.34 

Tin 1.33  50.44 

Aluminum 0. 10  86.49 

Copper  enters  readily  into  combination  with  the  constituents 
of  rubber  insulation  and  must  be  coated  with  a  protective  such 
as  tin,  which  is  not  easily  attacked. 

Copper  is  easily  soluble  in  nitric  acid,  aqua  regia  and  strong 
boiling  sulphuric  acid;  and  in  diluted  sulphuric  acid,  when  ex- 
posed to  the  air,  it  dissolves  slowly. 

The  tensile  strength  of  annealed  copper  is  usually  about  30,000 
Ib.  per  sq.  in.,  but  when  it  is  hard-drawn  or  medium  hard-drawn, 
its  strength  is  increased  to  50,000  and  65,000  Ib.,  depending  upon 
the  size  of  the  wire. 

Table  IX  gives  the  average  values  of  breaking  weight  for 
various  sizes. 


TABLE  IX. — TENSILE  STRENGTH  OP  PURE  COPPER  WIRE  IN  POUNDS 


Hard-drawn 

Annealed 

Hard-drawn 

Annealed 

Size 
B.  &S. 

Actual 

Average 
per  sq. 

Actual 

Average 
per  sq. 

Size 
B.  &S. 

Actual 

Average 
per  sq. 

Actual 

Average 
per  sq. 

in. 

in. 

an. 

in. 

0000 

8,260 

49,700 

5,320 

32,000 

7 

1,050.0 

64,200 

556.0 

34,000 

000 

6,550 

49,700 

4,220 

32,000 

8 

843.0 

65,000 

441.0 

34,000 

00 

5,440 

52,000 

3,340 

32,000 

9 

678.0 

66,000 

350.0 

34,000 

0 

4,530 

54,600 

2,650 

32,000 

10 

546.0 

67,000 

277.0 

34,000 

1 

3,680 

56,000 

2,100 

32,000 

12 

343.0 

67,000 

174.0 

34,000 

2 

2,970 

57,000 

1,670 

32,000 

14 

219.0 

68,000 

110.0 

34,000 

3 

2,380 

57,600 

1,323 

32,000 

16 

138.0 

68,000 

68.9 

34,000 

4 

1,900 

58,000 

1,050 

32,000 

18 

86.7 

68,000 

43.4 

34,000 

5 

1,580 

60,800 

884 

34,000 

19 

68.8 

68,000 

34.4 

34,000 

6 

1,300 

63,000 

700 

34,000 

20 

54.7 

68,000 

27.3 

34,000 

Many  experiments  have  been  made  determining  the  'effect  of 
temperature  on  the  tensile  strength  of  copper,  and  a  summary  of 
the  results  may  be  stated  as  follows: 

Up  to  about  400°F.  the  loss  in  strength  is  about  10  per  cent. ; 


CABLES  105 

at  500°F.  it  is  about  16  per  cent,  and  above  500°F.  it  is  so  great 
as  to  make  the  metal  almost  useless. 

As  the  conductivity  of  any  one  wire  will,  in  general,  differ 
from  that  of  any  other,  it  is  necessary  in  comparing  or  specifying 
wires  to  refer  to  some  standard. 

The  present  practice  in  copper  specifications  for  cable  work, 
is  to  refer  to  the  standardization  rules  of  A.I.E.E.  of  which  the 
following  shall  be  taken  as  normal  values  of  standard  annealed 
copper. 

1.  At  a  temperature  of  20°C.,  the  resistance  of  a  wire  of  standard  annealed 
copper,  1  meter  in  length,  and  of  a  uniform  section  of  1  sq.  mm.  is  ^g  onm  = 
0.017241 ohm. 

2.  At  a  temperature  of  20°C.,  the  density  of  standard  annealed  copper  is 
8.89  grams  per  c.c. 

3.  At  a  temperature  of  20°C.,  the  "constant  mass"  temperature  coeffi- 
cient of  resistance  of  standard  annealed  copper  measured  between  two  poten- 
tial points  rigidly  fixed  to  the  wire  is  0.00393  =  Ms 4- 45   •  •  •  •  Per  degree 
Centigrade. 

4.  As  a  consequence,  it  follows  from  (1)  and  (2)  that,  at  a  temperature  of 
20°C.,  the  resistance  of  a  wire  of  standard  annealed  copper  of  uniform  sec- 
tion, 1  meter  in  length,  and  weighing  1  gram,  is  (^s)  X  8.89  =  0.15328  . . . 
ohm. 

Table  X  gives  a  comparison  of  wire  gages  of  the  Brown  & 
Sharpe,  or  American  ("B.  &  S."),  the  Birmingham  (B.W.G.) 
and  the  British  Standard  (S.W.G.)  wire  gages. 

In  Table  XI  is  given  the  diameter,  weight  and  resistance  of 
copper  wires. 

The  following  Table  XII  gives  data  regarding  standard  con- 
centric strands  of  different  sizes  of  cable,  as  recommended  by 
the  General  Electric  Co. 

The  area  of  the  finished  cable  is  that  of  the  individual  wires 
cut  at  right  angles  to  their  axes,  when  laid  straight,  multiplied  by 
the  number  of  wires  in  the  cables.  Special  attention  is  called 
to  this  point,  since  in  some  cases  the  area  of  the  individual  wires 
is  figured  as  if  cut  after  twisting,  i.e.,  on  the  "bias,"  thus  using  a 
figure  larger  than  the  actual  area  of  the  finished  conductor,  and 
results  in  a  cable  having  less  copper  than  if  the  area  was  correctly 
figured. 

Insulating  Wall. — The  principal  materials  used  for  insulating 
power  cables  are  rubber,  saturated-paper  tapes,  varnished  cam- 
bric or  cloth  and  graded  insulation  usually  consisting  of  a 
combination  of  the  foregoing. 


106     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


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CABLES  107 

TABLE    XI. — DIAMETER,    WEIGHT    AND    RESISTANCE    OP    COPPER    WIRE 


Weight,  bare  wire 

Resistance  at  75°F. 

No. 
B.&S. 

Diame- 
ter, mils 

Area,  cir- 
cular mils 

Pounds 
per  1,000 
ft. 

Pounds 
per 
mile 

Ohms 

i.oSTft. 

Ohms 
per  mile 

Feet 
per  ohm 

0000 

460.000 

211,600.00 

640.73 

3,383.0400 

0.04904 

0.25891 

20939  .  2000 

000 

409.640 

167,805.00 

508.12 

2,682.8500 

0.06184 

0.32649 

16172.1000 

00 

364.800 

133,079.00 

402.97 

2,127.6600 

0.07797 

0.41168 

12825.4000 

0 

324.950 

105,592.50 

319.74 

1,688.2000 

0.09827 

0.51885 

10176.4000 

1 

289.300 

83,694.50 

253.43 

1,338.1000 

0.12398 

0.65460 

8066.0000 

2 

257.630 

66,373.20 

200  .  98 

1,061.1700 

0.15633 

0.82543 

6396.7000 

3 

229.420 

52,633.50 

159.38 

841.5000 

0.19714 

1  .  04090 

5072.5000 

4 

204.310 

41,742.60 

126.40 

667.3800 

0.24858 

1.31248 

4022.9000 

5 

181.940 

33,102.20 

100.23 

529.2300 

0.31346 

1  .  65507 

3190.2000 

6 

162.020 

26,250.50 

79.49 

419.6900 

0.39528 

2.08706 

2529.9000 

7 

144.280 

20,816.70 

63.03 

332.8200 

0.49845 

2.63184 

2006.2000 

8 

128.490 

16,509.70 

49.99 

263  .  9600 

0.62849        3.318431    1591.1000 

9 

114.430 

13,094.20 

39.65 

209.3500 

0.79242        4.18400 

1262.0000 

10 

101.890 

10,381.60 

31.44 

165.9800 

0.99948 

5.27726 

1000  .  5000 

11 

90.742 

8,234.11 

24.93 

131  .  6500 

1  .  26020 

6.65357|     793.5600 

12 

80.808 

6,529.94 

19.77 

104.4000 

1  .  58900 

8.  39001  i      629.3200 

13 

71.961 

5,178.39 

15.68 

82.7920 

2  .  00370 

10.57980      499.0600 

14 

64.084 

4,106.76 

12.44 

65.6580 

2.52660 

13.34050 

395.7900 

15 

57.068 

3,256.76 

9.86 

52.0690 

3.18600 

16.82230 

313.8700 

16 

50.820 

2,582.67 

7.82 

41.2920 

4.01760 

21.21300 

248.9000 

17 

45.257 

2,048.20 

6.20 

32.7460 

5.06600 

26.74850 

197.3900 

18 

40.303 

1,624.33 

4.92 

25.9700 

6.38800 

33  .  72850 

156.5400 

19 

35.890 

1,288.09 

3.90 

20.5940 

8.05550 

42.53290 

124.1400 

20 

31.961 

1,021.44 

3.09 

16.3310 

10.15840 

53.63620 

98.4400 

21 

28.462 

810.09 

2.45 

12.9520 

12.80880 

67.63020 

78.0700 

22 

25.347 

642.47 

1.95 

10.2720 

16.15040 

85.27430 

61.9200 

23 

22.571 

509.45 

1.54 

8.1450 

20.36740 

107.54000 

49  .  1000 

24 

20.100 

404.01 

1.22 

6.4593 

25.68300 

135.60600 

38.9400 

25 

17.900 

320.41 

0.97 

5.1227 

32.38330 

170.98400 

30.8800 

26 

15.940 

254.08 

0.77 

4.0623 

40.83770 

215.62300 

24.4900 

27 

14.195 

201  .  50 

0.61 

3.2215 

51.49520 

271.89500 

19.4200 

28 

12.641 

159.80 

0.48 

2.5548 

64.93440 

342.85400 

15.4000 

29 

11.257 

126.72 

0.38 

2.0260 

81.88270 

432.34100 

12.2100 

30 

10.025 

100.50 

0.30 

1  .  6068 

103.24500 

545.13300 

9  .  6860 

31 

8.928 

79.71 

0.24 

1  .  2744 

130.17600 

687.32700 

7.6820 

32 

7.950 

63.20 

0.19 

1.0105 

164.17400 

866.83700 

6.0910 

33 

7.080 

50.13 

0.15 

0.8014 

207.00000 

1092.96000 

4.8310 

34 

6.304 

39.74 

0.12 

0.6354 

261.09900 

1378.60000 

3.8300 

35 

5.614 

31.52 

0.10 

0.5039 

329.22500 

1738.31000 

3.0370 

36 

5.000 

25.00 

0.08 

0.3997 

415.04700 

2191.45000 

2.4090 

37 

4.453 

19.83 

0.06 

0.3170 

523.27800 

2762.91000 

1.9110 

38 

3.965 

15.72 

0.05 

0.2513 

660.01100 

3484.86000 

1.5150 

39 

3.531 

12.47 

0.04 

0.1993 

832.22800 

4394.16000 

1  .  2020 

40 

3.144 

9.88 

0.03 

0.1580 

1049.71800  5542.51000 

0.9526 

If  the  insulating  body  is  of  paper,  it  is  necessary  to  saturate 
it  with  an  insulating  compound  and  the  character  of  the  com- 
pound is  of  utmost  importance  in  determining  the  quality  and 
permanence  of  the  cable.  In  varnished-cloth  insulation,  specially 
prepared  cotton  fabric,  coated  on  both  sides  with  multiple  films 
of  insulating  varnish  is  used. 

Paper  and  varnished-cloth  insulation,  being  composed  of 
staple  commercial  fabrics,  impregnated  with  compound  of  well- 


108     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


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CABLES  109 

known  oils,  etc.,  are  not  readily  susceptible  to  adulteration  or 
imitation,  and  consequently  do  not  suffer  much  in  quality  from 
attempts  by  the  manufacturers  to  lessen  the  cost  of  production. 

Rubber  compounds,  on  the  other  hand,  being  made  of  any 
material  mixed  with  any  amount  or  grade  of  rubber,  are  easily 
adulterated  and  even  imitated.  The  extent  to  which  this  is 
sometimes  carried  makes  it  necessary  for  engineers  to  insist 
on  complete  mechanical  and  electrical  tests  of  the  compound. 

Rubber  Insulation. — Rubber-producing  trees  and  vines  of  one 
kind  or  another  are  found  in  all  tropical  countries.  Various 
grades  of  crude  rubber  are  known  by  the  name  of  the  country  or 
seaport  whence  they  come;  hence  the  terms  "Para,"  "Ceylon," 
etc.,  as  names  of  the  particular  grades  of  rubber.  In  the  prepara- 
tion of  rubber  for  insulating  purposes,  the  first  step  is  to  free  it 
from  all  impurities,  which  is  done  by  passing  it  between  corru- 
gated steel  rolls,  revolving  at  different  speeds  and  under  a  constant 
stream  of  water.  In  this  manner  the  rubber  is  washed  and  pre- 
pared in  sheets  ready  to  be  dried.  As  crude  rubber  is  affected  very 
much  by  the  changes  in  temperature  and  readily  oxidizes  in  the 
uncured  state,  the  rubber  must  be  compounded  with  other  mate- 
rials to  obtain  the  properties  needed  in  the  insulation  of  a  wire. 
Compounding  consists  chiefly  of  adding  other  substances,  such 
as  powdered  minerals,  including  a  small  percentage  of  sulphur. 
After  the  crude  rubber  has  been  warmed  to  a  plastic  condition 
in  heated  mixing  rolls,  it  is  thoroughly  kneaded  until  the  resulting 
compound  is  homogeneous  in  nature  and  of  suitable  physical 
condition  for  the  work  that  is  expected  of  it.  Another  reason 
for  compounding  is  that  the  cost  of  pure  rubber  for  insulating 
purposes  is  excessive.  The  matter  of  compounding  is  of  prime 
importance  and  requires  exhaustive  tests  and  experiments  to 
develop  a  suitable  insulating  material  for  various  conditions  of 
service.  Compounded  rubber  before  vulcanizing  is  plastic  and 
cohesive,  and  carr  be  shaped  into  any  form  desired.  In  order  to 
apply  it  to  a  wire,  two  different  methods  are  commercially  em- 
ployed; in  one  a  machine  similar  to  a  lead  press  is  used  and  the 
rubber  is  forced  by  a  revolving  worm  into  a  closed  chamber  at 
high  pressure,  the  wire  entering  this  chamber  through  a  nozzle 
of  its  own  diameter  and  leaving  from  a  nozzle  having  the 
diameter  of  the  intended  insulation.  The  wire  thus  comes  out 
with  a  seamless  coat  of  rubber,  forced  on  at  high  pressure. 

In  the  other  method  of  application,  the  rubber  is  sheeted  on 


110     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

a  calendar  having  heavy  smooth  rolls,  and  the  sheets  thus  made 
are  cut  into  narrow  strips,  the  width  and  thickness  of  which 
depend  on  the  wire  to  be  insulated,  and  the  number  of  covers  to 
be  used.  By  this  method  a  wire  is  passed  between  two  or  more 
curved  rolls,  running  in  tangent  to  each  other.  As  the  wire 
enters  each  pair  of  rolls,  strips  of  rubber  enter  at  the  same 
time  and  the  grooves  form  a  uniform  thickness  of  rubber  about 
the  wires,  the  edges  meeting  in  a  continuous  seam. 

Surplus  rubber  is  cut  off  the  rolls  and  the  seams,  being  made 
between  two  pieces  of  the  same  unvulcanized  cohesive  stock 
under  pressure,  become  invisible  in  the  wire,  and  can  be  deter- 
mined only  by  a  ridge  along  the  insulation. 

In  the  process  of  vulcanization,  the  rubber  at  the  seams  is 
kneaded  together  so  that  the  rubber  at  this  point  is  as  dense  and 
homogeneous  as  at  any  other  part  of  the  insulation. 


FIG.  54. — Crude  rubber. 

Good  rubber  compound  will  last  indefinitely  in  pure  or  salt 
water,  but  if  the  water  contains  sewage,  acids,  oils,  or  other 
destroying  agents,  it  will  have  a  short  life  unless  protected  with 
some  outer  covering,  such  as  a  lead  sheath. 

In  order  to  vulcanize  rubber  compounds,  they  are  subjected 
to  temperatures  somewhat  above  the  melting  point  of  sulphur, 
which  temperatures  are  usually  obtained  by  steam  under  pres- 
sure. This  operation  causes  the  sulphur  in  the  compound  to 
chemically  unite  with  the  rubber  and  other  ingredients  with  the 
result  that  the  rubber  is  no  longer  plastic;  it  becomes  firm,  strong, 
elastic,  susceptible  neither  to  heat  nor  cold,  and  not  readily 
affected  at  ordinary  temperatures  by  the  usual  solvents  of  unvul- 
canized rubber.  Its  mechanical  properties  depend  considerably 
on  the  time  and  temperature  of  vulcanization,  as  well  as  the 
amount  of  sulphur  used.  In  producing  high-grade  insulation, 
proper  vulcanization  is  fully  as  important  as  the  selection  of  the 
crude  materials.  Rubber  insulation  is  usually  protected  by  a 


CABLES  111 

winding  of  tape  or  braid,  or  a  tape  and  one  or  more  braids, 
depending  upon  the  class  of  service  for  which  it  is  to  be  used. 
When  used  for  station  work  it  is  sometimes  provided  with  an 
outer  braid  of  asbestos  or  other  form  of  flameproof  covering,  to 
serve  as  a  fire  protection.  When  installed  in  underground  con- 
duits where  it  is  subjected  to  the  severest  conditions,  it  should  be 
covered  with  a  lead  sheath. 

Paper  Insulation. — The  use  of  paper-insulated  cables  for  elec- 
tric light  and  power  work  is  rapidly  increasing,  and  when  prop- 
erly constructed  and  installed  such  cables  give  excellent  service. 

Various  kinds  of  paper  have  been  used  for  cable  insulation; 
the  extremes  of  quality  are  represented  by  that  made  from  wood 
pulp,  which  is  the  poorest,  and  that  made  from  manila  rope  fiber, 
which  is  the  best.  Between  these  extremes  there  are  combina- 
tions of  wood  pulp  with  jute,  jute  with  manila  fiber  and  wood 
pulp,  jute  and  manila  fiber.  A  paper  containing  any  appre- 
ciable amount  of  pulp  will  "felt  down"  when  saturated  with 
insulating  oils.  In  other  words,  the  fibers  of  the  paper  stand 
up  before  saturation,  giving  a  thickness  of  insulating  wall,  which 
is  greatly  diminished  during  impregnation;  because  of  this  "felt- 
ing down"  even  the  most  tightly  wound  insulations  composed  of 
pulp  paper,  will  be  found  quite  loose  after  saturation.  Wood 
fiber  or  pulp  paper  is  apt  to  be  injured  during  the  drying  process 
to  which  it  is  subjected  before  impregnation,  and  it  has  been 
known  to  rot  badly  under  the  influence  of  certain  of  the  substances 
used  in  the  impregnating  solution.  A  paper  containing  any 
appreciable  amount  of  jute,  either  alone  or  in  combination  with 
pulp  and  manila,  will  have  practically  all  the  disadvantages  of 
pulp  paper  and  in  addition  the  jute  will  saturate  very  slowly, 
which  sometimes  may  result  in  an  unevenly  saturated  cable. 
Manila-rope  paper  is  free  from  this  objection  and  its  structure  is 
hard,  close  and  even.  It  may  be  dried  perfectly  without  loss 
of  strength  and  will  not  rot  under  the  action  of  properly  prepared 
impregnating  oils. 

Manila-rope  paper  of  the  very  highest  grade  should  be  used 
in  all  paper-insulated  cable.  The  impregnating  oils  now  used 
by  the  majority  of  cable  manufacturers  consist  of  solutions  of 
rosin  and  rosin  oil,  and  solutions  of  rosin  and  petroleum  oil,  or 
a  mixture  of  these  solutions.  Commercial  rosin,  as  ordinarily 
found  on  the  market,  is  a  mixture  of  what  may  be  termed  rosin, 
some  undecomposed  turpentine  gum,  some  water,  acetic  acid  and 


112     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

butyric  acid,  together  with  light  turpentine  naphthas  and  turpen- 
tine. These  impurities  are  found  to  a  much  larger  extent  in 
second-run  rosin  oil.  The  method  of  preparing  rosin  oil  for  im- 
pregnation varies  with  different  manufacturers  in  accordance 
with  their  particular  formula,  and  the  lack  of  uniformity  in 
commercial  rosin  oil  requires  that  great  care  be  taken  in  the 
preparation  of  the  oil  for  insulating  purposes.  The  dielectric 
value  of  paper,  depends  not  only  on  the  quality  of  the  paper  and 
the  manner  of  applying  it  to  the  conductor,  but  to  a  great  extent 
upon  the  composition  of  the  insulating  compound.  Increasing 
the  fluidity  of  the  compound  within  certain  limits  will  improve 
the  puncture  test  and  will  increase  the  flexibility  of  the  cable,  but 
will  reduce  the  megohm  tests  and  vice  versa.  A  dense,  thick 
compound  will  result  in  a  very  stiff  cable,  but  one  having  a  higher 
insulation  resistance.  The  insulation  of  such  a  cable  is  apt  to 
crack  or  break  if  bent  at  a  low  temperature.  In  the  preparation 
of  paper-insulated  cables  automatic  machines  are  employed  to 
wind  narrow  strips  of  paper  spirally  around  the  conductors 
until  there  are  enough  layers  to  secure  the  requisite  dielectric 
strength.  If  the  cable  is  to  consist  of  two  or  more  conductors, 
the  necessary  number  of  conductors,  each  encased  in  its  wrapping 
of  paper,  are  laid  up  together  and  the  whole  encased  in  an  outer 
wrapping,  or  belt,  composed  of  additional  layers  of  paper. 

Before  the  outer  wrapping  of  paper  is  applied,  the  cable  is 
filled  with  jute  laterals  to  make  the  whole  cylindrical.  For 
high-tension  cables  some  manufacturers  use  a  fine  grade  of  twisted 
tissue  paper  in  place  of  the  jute  laterals.  The  cable,  after  being 
insulated,  is  placed  in  the  vacuum  drying  and  impregnating 
tanks.  Here  every  particle  of  moisture  and  air  should  be  re- 
moved even  from  its  inner  interstices,  and  the  hot  impregnating 
oil  is  forced  under  pressure  into  every  crevice  filling  the  pores  of 
the  paper  and  making  it  one  homogenous  structure.  The 
cable  is  then  put  through  a  hydraulic  press  and  covered  with  a 
closely  fitting  lead  sheathing  so  as  to  exclude  all  air  and  moisture 
and  to  retain  the  insulating  compound.  Paper  cables  are 
generally  cheaper  and  have  a  lower  electrostatic  capacity  than 
rubber  or  varnished-cambric  cables.  The  insulation  is  strong 
and  uniform  in  quality  and,  except  when  frozen  solid,  is  quite 
flexible.  Paper  cables  can  be  worked  safely  at  higher  tempera- 
ture than  can  other  kinds,  but  experience  has  demonstrated  that 
their  usual  life  is  determined  by  the  integrity  of  the  lead  sheath. 


CABLES  113 

Paper  is  less  liable  than  rubber  to  deterioration  from  excessive 
electrostatic  strains;  in  fact,  paper-insulated  cables,  when 
properly  constructed  and  sheathed,  can  be  recommended  as  the 
best  for  most  conditions. 

Varnished -cambric  Insulation. — Varnished-cambric  cables 
are  made  by  winding  strips  of  even-varnished  cotton  or  muslin 
served  separately  about  the  conductor  in  a  sufficient  number  of 
smooth,  tightly  drawn  layers  to  make  the  required  thickness  of 
dielectric.  It  is  customary  to  place  a  separator  of  treated  paper, 
cloth  or  rubber  over  the  copper  core  to  prevent  any  possible 
action  of  the  varnished- cambric  film  on  the  copper,  and  over  the 
separator  a  taped  strip  of  fabric  which  has  been  coated  with 
special  insulating  varnish.  The  dielectric  strength  of  this 
material  is  very  high,  as  single  thicknesses  of  cotton  well-treated 
with  varnish  will  withstand  potentials  of  approximately  10,000 
volts  for  5  sec.,  depending  upon  the  number  of  coats  of  varnish 
with  which  the  cloth  has  been  treated. 

The  varnish  prevents  the  tape  from  unwrapping  when  the 
cable  is  cut  and  permits  the  adjoining  layers  of  varnished  cam- 
bric to  slide  upon  each  other.  It  also  prevents  capillary  absorp- 
tion of  moisture  between  the  layers  of  tape,  seals  any  possible 
skips  in  films  and  precludes  air  spaces. 

In  multiple-conductor  cables  it  is  usual  to  place  a  portion  of  the 
required  thickness  of  insulation  in  the  form  of  a  belt  about  the 
core  of  conductors  as  is  the  case  in  paper  cables.  This  class  of 
cables  is  in  general  more  flexible  than  paper  cable,  more  imper- 
vious to  moisture  and  lower  in  cost  than  rubber  cables,  and  can 
be  used  for  station  work  without  lead  sheathing.  It  is  especially 
suitable  for  the  insulation  of  wire  and  cables  for  generators, 
motors  and  transformer  leads,  for  high-  and  low-tension  switch- 
board connections  and  wherever  the  following  conditions  are  to 
be  met  in  service:  namely,  moisture,  oil  drippings,  or  spasmodic 
increases  of  voltage  of  considerable  amount  but  of  short  duration. 

Where  this  type  of  cable  is  to  be  used  in  locations  where  it  is 
likely  to  be  submerged  in  water,  it  should,  of  course,  be  used  with 
a  lead  cover,  since  it  has  been  found  that  no  material  suitable  for 
wire  or  cable  insulation  is  permanently  lasting  in  non-leaded 
form  when  subjected  to  alternating  periods  of  heat  and  cold, 
wetness  and  dryness.  The  jointing  of  varnished-cambric  cables 
is  simpler  than  that  of  paper-insulated  cables  as  the  insulation 
of  the  former  does  not  absorb  moisture  and,  not  being  attacked 

8 


114     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

by  mineral  oil,  is.  particularly  adapted  for  use  in  connecting  to 
apparatus  submerged  in  oil,  such  as  switches  and  transformers. 
It  can  be  operated  at  a  temperature  higher  than  rubber  insula- 
tion but  not  quite  as  high  as  impregnated  paper  insulation. 
When  the  cable  is  to  be  used  on  insulators  or  through  insulating 
bushings,  and  exposed  only  to  such  moisture  as  is  held  in  sus- 
pension in  the  surrounding  air,  the  lead  cover  is  usually  replaced 
by  one  or  more  coverings  of  a  weatherproof,  flameproof  or 
asbestos  braid. 

Graded  Insulation.  —  For  exceptionally  high -voltage  work 
graded  insulation  has  been  employed  and  insulating  material 
having  different  capacities  has  been  used. 

It  is  a  well-known  fact  that  the  potential  gradient  of  insulated 
wire  is  much  higher  in  that  portion  of  the  insulation  near  the 
conductor  than  in  the  outer  layers;  and  the  fall  of  potential  across 
a  series  of  insulators  of  varying  specific  inductive  capacity  is 
inversely  proportional  to  those  capacities.  Cables  insulated 
with  two  or  more  materials  so  proportioned  as  to  their  relative 
thickness  and  specific  inductive  capacities  as  to  take  advantage 
of  this  law,  have  been  on  the  market  for  some  time  and  the 
advantages  to  be  secured  are  that  a  smaller  diameter  of  cable 
may  be  used  with  the  same  factor  of  safety  or  a  cable  may  be 
operated  at  a  higher  voltage,  the  outside  diameter  and  factor  of 
safety  remaining  the  same.  Cables  have  also  been  constructed 
with  rubber  and  paper,  or  rubber  and  cambric  insulation,  not 
with  the  view  of  obtaining  the  results  to  be  secured  by  grading, 
but  primarily  for  the  purpose  of  reducing  the  cost.  In  some 
cases  multiple-conductor  cables  have  been  insulated  with  a 
covering  of  paper  or  varnished  cloth  on  the  individual  conductor 
and  a  reinforced  rubber  jacket,  the  outer  rubber  jacket  being 
made  up  of  several  layers  of  rubber  and  cloth  as  a  protection 
against  moisture. 

In  ordinary  underground  work  the  use  of  graded  cables  is 
unnecessary  and  the  cost  of  such  cable  apparently  is  unwarranted 
except  in  special  cases.  For  more  detail  information  on  the 
subject  of  the  grading  of  cables,  the  reader  is  referred  to  the 
Transactions  of  the  American  Institute  of  Electrical  Engineers, 
vol.  29,  part  2,  page  1553,  "  Potential  Stresses  in  Dielectrics," 
by  Harold  S.  Osborne. 

Lead  Covering. — In  order  to  protect  the  insulation  of  cables 
from  injurious  effects  common  to  most  underground  systems, 


CABLES  115 

and  provide  a  protection  of  the  insulation  from  mechanical 
injury,  they  should  be  covered  with  a  lead  sheath.  While  rubber- 
insulated  cables  have  been  used  in  a  limited  way  without  a 
metallic  covering,  it  is  not  considered  good  engineering  practice 
to  use  such  cables  in  installations  of  a  permanent  character, 
as  the  dependable  life  of  the  insulation  does  not  exceed  10  years; 
whereas  the  same  insulation,  if  protected  by  a  lead  sheath,  would 
last  indefinitely. 

Lead,  or  a  composition  of  lead  and  tin,  is  the  most  usual 
material  for  sheathing  in  this  country. 

While  lightning,  electrolysis,  heat,  long-continued  vibrations 
and  mechanical  injuries  have  been  considered  about  the  only 
cause  for  breakdown  or  disintegration  of  the  lead  sheaths,  there 
are  cases  on  record  where  the  lead  has  been  destroyed  by  a  species 
of  lead-eating  insect.  These  insects  have  been  found  in  Australia 
and  in  the  southeastern  portion  of  the  United  States.  An  inter- 
esting paper  on  this  subject  was  read  before  the  International 
Congress  of  Electrical  Engineers,  at  the  Convention  in  St.  Louis, 
in  1904,  by  Mr.  John  Hesketh. 

Lead  is  the  heaviest  metal  used  to  any  large  extent  for  com- 
mercial purposes,  and  the  only  metal  used  for  the  protection 
of  hygroscopic  insulating  media.  It  is  not  used  in  a  chemically 
pure  state  for  commercial  purposes;  and  the  slight  traces  of 
arsenic,  antimony,  copper,  tin,  etc.,  which  are  sometimes  found 
in  the  extra  high-grade  lead  used  for  pipe  and  cable  sheaths  are 
rather  a  benefit  than  an  objection,  as  they  tend  to  slightly  harden 
the  metal.  Lead  is  also  hardened  by  hammering,  but  easily 
regains  its  original  softness  on  being  annealed. 

When  lead  is  alloyed  with  small  percentages  of  tin,  its  melting 
point  is  lowered  and  its  hardness  and  tensile  strength  increased. 
The  melting  point  continues  to  decrease  with  increasing  amounts 
of  tin  up  to  a  critical  value  of  63  per  cent,  when  the  alloy  then 
becomes  a  definite  chemical  compound.  Further  addition  of  the 
tin  results  in  an  increased  (instead  of  a  decreased)  melting  point. 

Lead,  as  is  well  known,  is  very  malleable,  but  lacking  in 
ductility. 

No  very  reliable  data  are  obtainable  as  to  the  tensile  and  com- 
pressive  strength  of  lead,  the  discrepancy  in  results  arrived  at 
by  different  experimenters  being  due,  doubtless,  to  the  influence 
of  impurities  and  temperature  variations. 

The  purest  commercial  lead  obtainable  is  generally  used  for  a 


116     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


sheathing.  It  is  sometimes  necessary  to  harden  and  strengthen 
the  lead  sheath  by  the  addition  of  1,  2  or  more  per  cent,  of  tin, 
but  it  is  a  question  as  to  whether  much  is  gained  by  this  addition. 
The  two  metals  do  not  alloy  uniformly  and  in  sheaths  where 
much  tin  is  used,  hard  or  brittle  sections  may  develop,  due  to  the 
segregation  of  one  of  the  metals.  The  purpose  of  tin  in  the  lead 
sheath  is,  not  to  prevent  chemical  action,  but  to  stiffen  the 
sheath  so  that  it  may  better  retain  its  cylindrical  form  when  the 
enclosed  core  is  soft,  as  is  the  case  in  some  of  the  dry-core  tele- 
phone cables.  It  appears  to  be  a  waste  of  money  to  put  tin  in  lead 
sheaths  of  cables  used  for  electric  light  and  power  purposes,  as 
the  introduction  of  tin  adds  at  least  10  per  cent,  to  the  cost  of  the 
cable  and  the  slight  advantages  gained  therefrom  do  not  warrant 
the  extra  expense.  If  tin  is  desired  as  a  protection  against 
chemical  action,  or  the  lead  cover,  the  proper  place  for  it  is  on,  not 
in,  the  latter,  for  that  places  it  where  it  will  do  the  most  good. 

As  to  the  thickness  of  lead,  especially  in  connection  with  paper- 
insulated  cables,  some  manufacturers  advocate  a  slightly  heavier 
thickness  than  for  rubber  cables  as  the  life  of  the  cable  is  entirely 
dependent  on  the  permanency  of  the  lead  sheath. 

The  following  Table  XIII  shows  the  thickness  of  lead  for  various 
outside  diameters  of  the  cable  core  as  determined  by  the  best 
engineering  practice. 

TABLE  XIII. — THICKNESS  OP  LEAD  SHEATH 


Diameter  of  core, 
mils 

Corresponding    thick- 
ness of  sheath,  in. 

Diameter  of  core, 
mils 

Corresponding  thick- 
ness of  sheath,  in. 

0-299 
300-699 
700-1,249 

«4 

%2 

H* 

1,250-1,999 
2,000-2,699 
2,700-over 

H 
& 

%2 

The  sheath  should  have  an  average  thickness  of  approximately 
that  indicated  in  the  foregoing  table,  and  the  minimum  thickness 
should  in  no  place  be  less  than  90  per  cent,  of  the  required 
thickness. 

Types  of  Cables. — Electric  light  and  power  cables  may  be 
divided  into  the  following  classes:  namely,  single  conductor, 
duplex,  concentric  and  multiple-conductor  cables  consisting  of 
three,  four  or  more  conductors  under  the  one  sheath  as  shown  in 
Fig.  55. 

Single-conductor  cables  are  most  commonly  used  for  low-ten- 


CABLES  117 

sion  electric-lighting,  power  and  arc-light  service,  but  they  are 
also  used  -under  special  circumstances  for  high-tension  trans- 
mission. For  railway  feeders  and  direct-current  power  mains, 
single-conductor  cables  are  almost  always  used,  as  the  size  of 
conductor  required  for  this  class  of  service  is  usually  too  large  to 
permit  the  installation  of  a  multi-conductor  cable  of  equal  con- 
ductivity in  a  single  duct.  In  general,  single-conductor  cable 
is  most  frequently  employed  for  service  mains  where  a  number  of 
taps  are  required.  Duplex  cables  are  employed  for  feeders 


Concentnc 


Conductor 


3~Conducfor 
Conductor 


FIG.  55. — Types  of  underground  cables. 

which  do  not  require  frequent  taps,  such  as  alternating-current, 
single-phase  circuits  where  both  legs  of  the  circuit  cover  the  same 
routes.  For  arc-light  circuits  or  portions  thereof,  or  for  low- 
pressure  distribution  mains,  duplex  cables  are  frequently  used. 
Relatively  less  duct  space  is  required  and  duplex  cables  are  safer 
to  handle  than  two  single-wire  cables  and  in  addition  are  less 
expensive  in  first  cost.  Double-  and  triple-concentric  cables 
have  the  same  advantage  as  just  stated  for  duplex  cable,  and  they 
are  preferable  in  large  conductor  sizes  where  the  side-by-side 
arrangement  of  duplex  cable  would  be  difficult  to  bend.  The 
concentric  arrangement  is  frequently  employed  for  large  feeders 
and  low-tension  Edison  direct-current  service  when  a  feeder  of 
750,000  cm.  or  larger  would  require  two  ducts,  if  single-con- 


118     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

ductor  cable  were  used.  Where  numerous  feeders  are  employed 
and  the  duct  space  is  limited,  this  item  is  of  much  importance. 

In  some  cases,  particularly  in  the  Edison  direct-current  feeder, 
pressure  wires  are  used  to  indicate  and  regulate,  at  the  station, 
the  pressure  or  difference  in  potential  existing  at  outlying  points. 
A  No.  14  or  No.  16  insulated  pressure  wire  can  be  incorporated 
at  some  suitable  point  in  the  cable,  generally  in  the  outer  layer 
of  the  stranded  conductor,  or  in  the  valleys  or  interstices  of 
bunched  cables  as  shown  in  Fig.  56. 

In  alternating-current  two-  and  three-phase  circuits,  feeders 
of  two,  three  and  four  conductors  are  preferable  on  account  of 
their  lower  cost.  For  this  class  of  service  paper-insulated  cables 
are  employed  as  they  are  considerably  cheaper  than  either  var- 
nished-cloth or  rubber-insulated  cables.  In  the  case  of  multiple- 
conductor  cables,  the  wires  are  twisted  together  with  a  suitable 


'Pressure  Mre 


Pffperlnsu/atfon 
Outer  Conductor 
'Inner  Corx/uc  tor 


FIG.  56. — Concentric  cable  with  pressure  wires. 

lay,  the  interstices  are  filled  with  jute  or  paper  laterals  to  make 
the  core  substantially  round,  and  a  further  covering  (called 
"the  belt")  of  the  same  insulating  material  is  placed  around  the 
core,  generally  to  the  same  thickness  as  the  insulation  around 
the  individual  wires.  In  the  case  of  rubber  cables  the  belt  is 
sometimes  made  of  paper  instead  of  rubber,  depending  upon  the 
pressure  at  which  it  is  to  be  used,  and  especially  if  it  is  intended 
for  comparatively  low  pressure.  Even  in  paper  cables  for  low- 
tension  service,  the  belt  is  not  always  made  of  the  same  thick- 
ness as  the  insulation  in  the  individual  wires,  but  for  high- 
tension  service,  the  usual  practice  is  to  " split"  the  insulation 
(from  which  these  cables  are  sometimes  spoken  of  as  cables  with 
"split  insulation")  equally  between  the  conductors  and  the  belt. 


CABLES  119 

When  it  is  desired  to  connect  multiple-conductor  cables  to 
overhead  lines,  single-conductor  cables  have  been  employed,  but 
with  multiple-conductor  pole  terminals,  as  described  in  another 
chapter,  the  use  of  multiple-conductor  cables  for  the  lateral  pole 
connection  is  now  rapidly  becoming  general  practice. 

In  single-conductor  cables,  or  an  alternating-current  system, 
carrying  heavy  loads,  there  is  apt  to  be  an  inductive  action  and 
the  magnetic  field  may  become  strong  enough  to  induce  an  appre- 
ciable difference  of  potential  between  the  lead  sheaths  of  single- 
conductor  cables  of  a  circuit,  resulting  in  the  flow  of  sufficient 
current  to  cause  damage  to  the  sheaths  where  they  come  into 
contact  with  each  other.  For  connections  to  subway  transform- 
ers, junction  boxes  and  manhole  switches,  single-conductor  cables 
are  used  to  tap  on  or  connect  to  the  multiple-conductor  feeders, 
as  they  facilitate  the  making  of  such  connections. 

Diameter  and  Length  of  Cables. — As  a  rule  cables  having  a 
diameter  of  over  3%  in.  should  not  be  specified  on  account  of  the 
difficulty  of  handling  and  drawing  into  the  conduits.  The  greater 
the  diameter,  the  greater  the  danger  of  the  lead  cover  buckling 
or  breaking  when  bent,  and  abrading  in  the  operation  of  pulling 
in.  For  underground  cables,  the  net  diameter  of  the  duct  will 
control  the  maximum  diameter  of  the  cable,  which  latter  should 
be  approximately  one-sixth  less  than  the  former,  and  in  no  case 
less  than  one-eighth  smaller  in  diameter.  A  margin  or  difference 
of  one-fourth  the  duct  diameter  represents  the  best  condition  for 
ease  and  safety  of  drawing  in  cables. 

Cable  may  be  made  in  almost  any  length,  but  it  is  desirable, 
on  account  of  manufacturing  operations,  to  confine  the  length  to 
certain  practical  economic  limits.  Extraordinary  lengths  re- 
quire the  temporary  adoption  of  extraordinary  methods  and  de- 
vices in  manufacture,  shipment  and  installation,  at  an  increased 
cost  quite  out  of  proportion  to  the  safer  and  simpler  expedient, 
practicable  in  most  cases,  of  making  a  few  more  splices  or  building 
a  few  more  manholes.  Cables  weighing  1  Ib.  or  less  per  ft.  can 
usually  be  supplied  in  lengths  of  2,500  to  3,500  ft.  on  a  single  reel, 
and  heavier  cables  in  approximately  inverse  proportions;  thus 
for  cables  weighing  6  Ib.  per  ft.,  the  reel  should  contain  something 
under  600  ft.  of  cable. 

Table  XIV  gives  the  maximum  length  in  feet  of  cable  that 
can  be  shipped  on  standard  reels. 


120     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


TABLE  XIV.— CABLE  REEL  DATA1 


Overall 
dia.  of 
cable,  in. 

Reel  No.  6, 
24  by  12  in 
max.  length, 
ft. 

Reel  No.  5, 
30  by  21  in. 
max.  length, 
ft. 

Reel  No.  4, 
48  by  24  in. 
max.  length, 
ft. 

Reel  No.  3, 
60  by  24  in. 
max.  length, 
ft. 

Reel  No.  2, 
60  by  41  in. 
max.  length, 

Reel  No.  1, 
66  by  41  in. 
max.  length, 
ft. 

0.25 
0.30 
0.35 
0.40 
0.45 
0.50 
0.55 
0.60 
0.65 
0.70 

0.75 
0.80 
0.90 
1.00 
1.10 
1.20 
1.30 
1.40 
.50 
.60 

.70 
.80 
.90 
2.00 
2.25 
2.50 
3.00 

2,000 
1,500 
1,100 
900 
600 
500 
400 
300 
300 
225 

200 

7,000 
4,800 
3,350 
2,500 
2,000 
1,750 
1,450 
1,200 
1,000 
850 

750 
700 
550 
400 

5,000 
4,500 
4,200 
3,400 
2,900 

2,700 
2,250 
2,000 
1,600 
1,200 
950 
750 
700 
650 

4,500 
4,000 

3,500 
3,100 
2,400 
2,100 
1,750 
1,400 
1,200 
975 
800 
750 

700 
625 
550 
460 
325 
275 
210 

4,200 
3,500 
2,800 
2,400 
1,950 
1,600 
1,500 

1,400 
1,250 
1,100 
920 
650 
550 
420 

3,900 
3,300 
2,800 
2,300 
2,100 
1,750 

1,650 
1,500 
1,225 
1,100 
850 
700 
525 

..... 



::::: 





Approximate  Maximum  Weight  of  Cable  per  Reel,  Ib. 

225 

650 

1,500 

3,100 

6,200 

8,000 

Approximate  Weight  of  Empty  Reel,  Ib. 

24 

70 

190 

345 

415 

465 

Approximate  Weight  of  Reel  with  Slats,  Ib. 

36 

100 

240 

495 

650 

760 

1  General  Electric  Co. 


For  example:  1,000  ft.  of  any  cable  %  in.  in  diameter  and  weigh- 
ing 650  Ib.  would  require  a  No.  5  reel. 

Fiber  Core  Cables. — Owing  to  the  fact  that  alternating  current 
flowing  in  large  cables  has  greater  density  on  the  surface  of  the 


CABLES 


121 


conductor  than  in  the  center  (so-called  skin  effect),  ordinary 
cable  will  not  carry  as  much  alternating  current  with  the  same 
temperature  rise  as  direct  current.  In  order  to  overcome  this 
it  is  advisable  on  single-conductor  cables,  700,000  cm.  and  larger 
for  60-cycle  circuits  and  1,250,000  cm.  and  larger  for  25-cycle 
circuits,  to  make  up  the  cable  with  a  fiber  core  with  the  copper 
stranded  around  it.  The  weight  of  the  copper  in  this  type  of 
cable  is  the  same  per  foot  as  in  an  ordinary  cable,  but  owing  to 
its  annular  cross-section  the  cable  is  much  more  efficient  in 
carrying  alternating  current  and  also  has  a  somewhat  greater 
current-carrying  capacity  due  to  the  larger  radiating  surface. 
These  copper  strands  can  be  insulated  with  any  desired  type  of 
insulation. 

Table  XV  gives  the  diameter  of  core  recommended  for  various 
sizes,  and  the  overall  diameter  as  well  as  the  ampere  capacity  at 
30°C.  and  60°C. 

TABLE   XV.— FIBER   CORE   CABLE   DATA1 


Size 

Dia.  fiber 
core,  in. 

No.  of  wires 
in  strand 

Size  wire  in 
strand,  in. 

Overall  dia. 
copper  core, 
in. 

Ampere  capacity 

30°C. 

60°C. 

2,000,000 

% 

210 

0.099 

2.065 

1,400 

1,750' 

1,750,000 

2^2 

210 

0.091 

.870 

1,300 

1,625' 

1,500,000 

iMe 

182 

0.091 

.780 

1,200 

1,500 

1,250,000 

91  6 

168 

0.086 

.590 

1,150 

1,400 

1,000,000 

^3 

98 

0.102 

.280 

900 

1,150 

800,000 

»Ha 

51 

0.125 

.100 

•  775 

925, 

700,000 

Hi 

51 

0.117 

0.990 

700 

830J 

1  General  Electric  Co. 

Transmission  Cables. — In  no  branch  of  the  underground-cable 
problem  have  the  conditions  been  more  difficult  than  in  that  of 
transmission  with  high-tension  current,  for  the  reason  that  the 
far  greater  pressure  considerably  increases  the  tendency  to  dis- 
rupt the  insulation,  allowing  the  current  to  escape  from  its  con- 
ductor. Great  difficulties  were  encountered,  and  failures  were 
experienced,  principally  due  to  inexperience  or  utter  disregard  of 
proper  care  on  the  part  of  those  in  charge  of  the  laying,  jointing, 
or  operating  of  the  cables,  but  each  failure  led  to  a  better  under- 
standing of  the  conditions  to  be  provided  for  and  the  invention 
and  adoption  of  the  means  of  overcoming  them,  so  that  now  it 
is  entirely  practicable  to  manufacture  and  install  cables  for  trans- 


122     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

mission  to  operate  at  25,000  and  30,000  volts.     Several  hundred 
miles  of  such  cables  are  now  in  successful  daily  operation. 

Transmission  lines,  which  are  usually  three-phase,  are  almost 
universally  of  three-conductor  cable  with  a  thickness  of  insulation 
on  each  conductor  sufficient  for  voltages  between  phases.  One 
of  the  first  installations  of  three-phase,  high-tension  cables  was 
made  in  St.  Paul,  Minn.,  in  1900.  The  highest  potential  used 
underground  prior  to  that  time  was  11,000  volts.  Since  this 
time  cables  of  25,000  and  30,000  volts  have  been  installed  in  a 
number  of  places.  In  certain  sections  of  Europe  extensive 
underground  cable  systems  operating  at  30,000  volts  have  been 
very  successful  and  results  obtained  by  certain  cable  manu- 
facturers through  the  use  of  improved  insulating  material  and 
processes  of  manufacture  definitely  indicate  that  satisfactory 
cable  may  now  be  obtained  to  operate  at  30,000  volts.  As  it  is 
both  inconvenient  and  expensive  to  change  the  maximum  voltage 
of  a  cable  system  once  established,  recognition  of  the  present 
situation  should  be  given  and  cables  purchased  for  future  exten- 
sion which  may  be  operated  at  the  highest  convenient  voltage. 

General  Cable  Data.— The  following  Table  XVI  gives  the 
working  and  test  voltages  for  any  size  cable  with  a  given  thickness 
of  insulation,  or  the  proper  thickness  of  insulation  may  be 
determined  for  various  voltages. 

The  working  voltages  in  the  foregoing  tabulation  are  based  on 
all  conductors  of  the  circuit  being  insulated.  For  three-phase 
"  Y  "-connected  circuits  with  grounded  neutral  with  three-con- 
ductor cables,  thickness  of  insulation  between  conductors  and 
ground  need  only  be  seven-tenths  of  that  between  conductors. 
The  required  thickness  of  insulation  can  be  placed  about  each 
separate  conductor  before  it  is  laid  up  into  the  core,  or,  as  is 
more  general,  especially  with  paper  and  varnished  cloth,  a  por- 
tion of  the  required  amount  of  insulation  can  be  placed  in  the 
form  of  a  belt  about  the  assembled  conductors.  This  latter 
method  makes  a  more  even  distribution  of  the  insulating  material 
and  is  the  one  most  commonly  used. 

The  approximate  outside  diameters  of  three-conductor  cables 
with  various  thickness  of  insulation  and  with  J^-in.  lead  sheath 
throughout  is  given  in  Table  XVII. 

The  largest  size  outside-diameter  cable  which  can  safely  and 
conveniently  be  installed  in  a  standard  3-in.  duct  is  approxi- 
mately 2.7  in.  It  will,  therefore,  be  noted  from  the  foregoing 


CABLES 


123 


TABLE   XVI. — WIRES   AND   CABLES 
Working  and  Test  Voltages1 


Kilovolts, 
work,  press. 

Sizes 

Thick., 
insulation 

Test  in  kilovolts 

At  factory 

After  installation 

5  min.  30  min. 

60min. 

5  min. 

30  min. 

60min. 

0.6 
0.6 
0.6 

14-2 
1-4/0 
225,000-500,000 

Me 

Ht 
Hi 

2.0 
2.0 
2.0 

1.6 
1.6 
1.6 

.3 
.3 
.3 

1.6 
1.6 
1.6 

1.3 
1.3 
1.3 

1.0 
1.0 
1.0 

0.6 
1.0 
1.0 

550,000-1,000,000 
12-2 
1-4/0 

9fe 

Hz 

2.0 
2.5 
2.5 

1.6 
2.0 
2.0 

.3 
.6 
.6 

1.6 
2.0 
2.0 

1.3 
1.6 
1.6 

1.0 
1.3 
1.3 

1.0 
1.0 
2.0 

225,000-500,000 
550,000-2,000,000 
10-4/0 

fa 
tit 

2.5 
2.5 
5.0 

2.0 
2.0 
4.0 

.6 
.6 
3.2 

2.0 
2.0 
4.0 

1.6 
1.6 
3.2 

1.3 
1.3 
2.5 

2.0 
2.0 
3.0 

225,000-500,000 
550,000-2,000,000 
8  and  larger 

%4 

5.0 
5.0 
7.5 

4.0 
4.0 
6.0 

3.2 
3.2 
4.8 

4.0 
4.0 
6.0 

3.2 
3.2 

4.8 

2.5 

2.5 
3.8 

4.0 
5.0 
6.0 

8  and  larger 
6  and  larger 
6  and  larger 

3/le 

H, 
M 

10.0 
12.5 
15.0 

8.0 
10.0 
12.0 

6.4 
8.0 
9.6 

8.0 
10.0 
12.0 

6.4 
8.0 
9.6 

5.1 
6.4 

7.7 

7.0 
9.0 
11.0 

5  and  larger 
5  and  larger 
4  and  larger 

Hi 

Me 

17.5 
22.5 
27.5 

14.0 
18.0 
22.0 

11.2 
14.4 
17.6 

14.0 
18.0 
22.0 

11.2 
14.4 
17.6 

9.0 
11.5 
14.1 

13.0 
15.0 
17.0 

4  and  larger 
3  and  larger 
3  and  larger 

1 

32.5 
37.5 
42.5 

26.0 
30.0 
34.0 

20.8 
24.0 
27.2 

26.0 
30.0 
34.0 

20.8 
24.0 
27.2 

16.6 
19.2 
21.7 

19.0 
21.0 
23.0 

2  and  larger 
2  and  larger 
1  and  larger 

^, 

47.5 
52.5 
57.0 

38.0 
42.0 
46.0 

30.4 
33.6 
36.8 

38.0 
42.0 
46.0 

30.4 
33.6 
36.8 

24.3 
26.8 
29.4 

25.0 

1/0  and  larger 

He 

62.5 

50.0 

40.0 

50.0 

40.0 

31.9 

Kilovolts  =  1,000  volts. 

Above  working  voltages  are  based  on  all  conductors  of  the  circuit  being  insulated.  For 
d.c.  600-volt  railway  single  conductor  use,  2000-volt  class.  For  three-phase  "  Y"  connected 
circuits  with  grounded  neutral  with  three-conductor  cables,  thickness  of  insulation  between 
conductors  and  ground  need  only  be  seven-tenths  of  that  between  conductors.  Tests  on 
such  cable  in  proportion  to  thickness  of  insulation:  Example,  three-phase  13,000-voIt  cir- 
cuit "  Y,"  neutral  grounded,  insulation  on  each  conductor  jHo  in.  (total  between  conductors 
H  in.),  outer  belt  Hz  in.  (total  j&j  in.);  test  pressure  at  factory  for  5  min.,  between  conduct- 
ors 32,500  volts,  each  conductor  to  earth  17,500  volts. 

1  General  Electric  Co.,  Bulletin  No.  4787. 


table  that  the  largest  conductor  size  for  %2  by  %%  cable  with  J^- 
in.  lead  (7,000  volts  working  pressure)  is  350,000  cm.;  whereas, 
for  i%2  by  l%2  and  >£-in.  lead  (25,000  volts  working  pressure) 


124     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


the  largest  conductor  size  to  be  installed  in  a  3-in.  duct  is  No.  4 
wire. 

TABLE  XVII. — APPROXIMATE  OUTSIDE  DIAMETERS  OP  THREE-CONDUCTOR 

COPPER  CABLES 

(^  Lead  Throughout) 

Insulation  Thickness  on  Each  Conductor,  and  Over  Bunch  Respectively 

Equal  to 


Sue 

%a  +  *$2 

M*  +  %i 

%2   +  %2 

9$2  +  ?ia 

1%2+l&» 

Diam. 

Diam. 

Diam. 

Diam. 

Diam. 

4 

1,735 

1,930 

2,129 

2,324 

2,717 

3 

1,795 

1,990 

2,189 

2,384 

2,777 

2 

1,864 

2,059 

2,258 

2,453 

2,845 

1 

1,950 

2,145 

2,344 

2,539 

2,933 

0 

2,038 

2,233 

2,432 

2,627 

3,020 

00 

2,137 

2,332 

2,531 

2,726 

000 

2,246 

2,442 

2,640 

2,839 

0000 

2,371 

2,567 

2,765 

2,960 

Cm. 

250,000 

2,472 

2,668 

2,866 

300,000 

2,588 

2,785 

2,983 

350,000 

2,700 

2,895 

400,000 

2,803 

3,000 

450,000 

2,898 

500,000 

2,988 

Tables  XVIII  and  XIX  give  the  thickness  of  insulation  as 
specified  by  the  cable  manufacturers  for  rubber,  paper  and 
varnished-cambric  insulation. 

TABLE  XVIII. — THICKNESS  OP  CAMBRIC  INSULATION1 


Normal  working  voltage 

Insulation  about  each 
conductor,  in. 

Insulation  about  three 
conductors,  in. 

7,000 

K* 

^2 

10,000 

%2 

9& 

13,000 

%2 

9*2 

17,000 

Jfa 

to 

20,000 

Mi 

*fc 

23,000 

»»« 

'%4 

25,000 

»H« 

1*4 

i  General  Electric  Co.     Bulletin  No.  4591. 


In  the  table  furnished  by  the  Safety  Insulated  Wire  &  Cable 
Co.  no  jacket  is  provided  with  the  rubber-insulated  cables  in- 
tended for  use  at  the  lower  voltages.  This  is  due  to  the  fact 
that  a  thin  rubber  jacket  will  be  reduced  in  thickness  by  the 


CABLES 


125 


pressure  from  the  insulated  conductors,  as  it  appears  to  be 
impossible  to  maintain  a  uniform  pressure  of  the  jute  and  the 
conductors  against  the  jacket. 

TABLE  XIX. — THICKNESS  OF  RUBBER  AND  PAPER  INSULATION. l 


Normal  working 
voltage 

Rubber  insulation 

Paper  insulation 

About  each 
conductor,  in. 

About  three 
conductors,  in. 

About  each 
conductor,  in. 

About  three 
conductors,  in. 

5,000 

Hi 

None 

Hi 

^2 

7,000 

Jfa 

None 

%2 

Hi 

10,000 

Hz 

H* 

%2 

Hi 

13,000 
17,000 

%2 

Hi 

%2 

%2 

20,000 

%* 

%2 

%2 

Hi 

25,000 

l%2 

%2 

!%2 

1%2 

30,000 

'Hi 

^ 

2J; 

1^2 

S.  I.  W.  &  C.  Co. 

TABLE  XX. — DATA  ON  PAPER  CABLE  OPERATION 


Company 

Line 
vol- 
tage 

Insu- 
lation 

Thickness  of  insulation  in  thou- 
sandths of  an  inch 

Between 
conduct- 
ors 

Between 
conduct- 
ors and 
ground 

Per  1,000  volts 

Neutral 
grounded 

Between 
conduct- 
ors 

Between 
conduct- 
ors and 
ground 

New  York  Edison  

6,600 
6,600 
6,600 
6,600 
6,600 
6,900 
9,000 
9,500 
11,000 
11,000 
11,000 
11,000 
11,000 
11,500 
13,000 
13,200 
13,200 
15,000 
20,000 
23,000 
25,000 
25,000 
26,400 

Paper 
Paper 
Paper 
Paper 
Paper 
Paper 
Paper 
Paper 
Paper 
Paper 
Paper 
Paper 
Paper 
Paper 
Paper 
Paper 
Paper 
Paper 
Paper 
Paper 
Paper 
Paper 
Paper 

312 
342 
312 
436 
312 
436 
375 
374 
436 
436 
436 
436 
406 
500 
375 
375 
436 
500 
562 
562 
562 
562 
562 

312 
342 
312 
343 
312 
436 
312 
374 
468 
436 
436 
375 
406 
406 
375 
375 
436 
437 
375 
375 
484 
406 
531 

47 
52 
47 
66 
47 
63 
42 
39 
40 
40 
40 
40 
37 
43 
29 
28 
33 
33 
28 
24 
22 
22 
21 

47 
52 
47 
52 
47 
63 
60 
39 
43 
40 
69 
59 
37 
35 
50 
28 
33 
29 
32 
28 
19 
16 
20 

No 
No 
No 
No 
No 
No 
Yes 
No 
No 
No 
Yes 
Yes 
No 
No 
Yes 
No 
No 
No 
Yes 
Yes 
No 
No 
No 

Brooklyn  Edison  
Phila.  Elec.  Co  
N.  Y.  Metropolitan  

St.  Louis.  .  .  . 

Boston  

Chicago.    .... 

Hartford     . 

New  York  Subway  

New  York  Manhattan  
Long  Is.  R.  R  

New  York  Central  
Niagara 

Buffalo 

Minneapolis  
Philadelphia  

P.  S.-N.  J  . 

Milwaukee 

Chicago  
Detroit  Edison  
St.  Paul..    . 

Montreal.  . 

P.  S.-N.  J  

126     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


It  is  rather  difficult  to  determine  mathematically  the  proper 
thickness  of  insulation  to  use  for  a  given  potential  and  it  is,  there- 
fore, better  to  rely  on  tables  furnished  by  cable  manufacturers. 
Certain  difficulties  in  the  manufacture,  such  as  unevenness  of 
the  application  of  insulation  on  the  conductors,  eccentric  placing 
of  the  insulation  and  mechanical  considerations  of  strength, 
make  such  tables  of  insulation  required  for  different  voltages 
and  sizes  of  conductors  more  valuable  and  reliable  than  formulae. 

As  illustrating  the  difference  of  opinion  among  engineers 
as  to  the  proper  factors  of  safety  to  use  in  the  design  of  high- 
voltage  cables,  the  following  tabulation  (Table  XX)  shows  the 


FIG.  57. — Sector-type  three-conductor  transmission  cable. 

practice  of  a  number  of  important  operating  companies  using 
three-conductor  high-tension  cables. 

Sector  Cables. — With  the  growth  of  electric  service  and  the 
increase  in  size  of  conductors  for  transmission  systems  the  maxi- 
mum size  of  three-conductor  cable  which  can  be  safely  installed 
in  a  duct  nominally  3  in.  in  diameter  has  been  reached.  To 
meet  this  condition  and  make  it  possible  to  install  cables  having 
larger  conductors  or  thicker  insulation,  cables  have  recently 
been  constructed  in  a  clover  leaf  or  sector  form,  as  illustrated  in 
Fig.  57. 

Cables  of  this  form  of  construction  have  been  in  use  in  Europe 
for  a  number  of  years,  but  American  manufacturers  have  taken 


CABLES 


127 


up  the  making  of  sector  cables  only  within  the  last  5  years.  This 
form  of  conductor  permits  of  a  more  economical  utilization  of  duct 
space  and  the  cable  is  slightly  less  expensive  than  round-conductor 
in  sizes  of  No.  000  B.  &  S.  gage  or  greater.  Several  large  central- 
station  companies  have  adopted  this  form  of  cable  for  transmis- 
sion purposes  where  it  has  been  impossible  to  secure  space  for 
large-sized  round-conductor  cables. 

Clover-leaf  or  sector  cable  in  sizes  under  No.  00  B.  &  S.  gage 
is  not  manufactured  to  any  extent,  due  to  the  fact  that  difficulty 
is  experienced  in  maintaining  the  shape  of  the  conductor  when 
forming  the  cable. 


-3.1 
-3.0 
-2.9 
•2.8 
-2.7 
-2.6 
-2.5 
-2.4 
-2.3 
-2.2 
-2.1 


222j^* 


200,000  300,000  400,000  500,000  500,000 

Copper  Area  of  each  of  Three  Conductors  in  Circular  Mils 

FIG.  58. — Relative  outside  dimensions  of  round  and  sector  cable  having  1  ^4- 
inch  insulation  on  each  conductor,  ^2-incn  belt  and-^£  inch  lead. 

In  determining  the  rating  for  the  various  sizes  of  sector  cable, 
it  should  be  noted  that,  due  to  its  shape,  a  larger  portion  of  the 
periphery  of  each  conductor  is  nearer  the  lead  sheath  than  in  an 
equivalent  round-conductor  cable.  This  allows  a  greater  radia- 
tion with  a  consequent  higher  current  rating  of  the  cable.  No 
fixed  standard  governing  the  carrying  capacity  of  cables  can 
be  given  as  this  depends  largely  on  the  conditions  governing 
heat  radiation.  The  position  of  cables  in  duct  lines,  the  nature  of 
the  soils  through  which  the  duct  lines  run,  and  their  exposure  to 
the  elements,  are  all  factors  to  be  considered  in  determining  the 
rating  of  a  cable.  Data  obtained  from  operating  companies  on 
sector  cable  is  given  in  Table  XXI,  the  information  being 


128     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


TABLE  XXI. — DATA  ON  SECTOR  CABLE  USED  BY  FIVE  LARGE  ELECTRIC- 
SERVICE  COMPANIES* 


Name  of 
company 

Amount, 
ft. 

Service, 
voltage 

Thickness  in 
H2  in.  of 
insulation 
around 

Conductor 
cross-sec- 
tion,   circ. 
mils 

Carrying 
capacity, 
permitted 

Each 
con- 
ductor 

Insu- 
lated 
Con- 
ductors 

New  York  Edi- 
son Co.1  

459,360 
163,680 

19,324.50 
14,127.10 
3,861.20 
141,472.51 
910.00 
72,284.10 
2,730.00 

8,000 
Same  to 
cable 
shell 

15,000 
Same  to 
cable 
shell 

7,500 
7,500 
7,500 
15,000 
15,000 
23,000 
23,000 

13,500 
6,600" 

4,600-volt 
trunk  line 
4,800-volt 
distribu- 
tion to 
overhead 
lines 

m 

7 

5^2 
6^3 

7* 
75 
8« 
S*4» 

88 

6 
6 

5 
5 

5 

7 

5 

p 

7 
8 
4 
8 

6 
6 

5 
5 

350,000 
350,000 

350,000 
350,000 
350,000 
350,000 
350,000 
350,000 
350,000 

350,000 

350,000 
2.78  to  2.89 
in.  outside 
diameter 

450,000 
450,000 

3,500  kva.,  with 
50  per  cent, 
overload 
for    1    hr.    at 
6,600  volts 
6,000  kva.,  with 
same  per  cent- 
age  of  over- 
load rating 

7,500  kva. 

3,000   kva.  « 
3,000   kva.« 

United     Electric 
Light  &  Power 
Co 

Public       Service 
Electric  Co.  of 
New  Jersey  
Brooklyn   Rapid 
Transit  Co.">.  .  . 

Detroit     Edison 
Co 

258,081.  4  1» 

200,000 
209,668 

64,416 
11,616 

1  Specifications  call  for  31  strands  per  conductor.     Thickness  of  sheath  is  \b  in.     Alter- 
nating-current test  voltage  for  5  min.  between  conductor  and  ground,  25,000  volts,  and  be- 
tween conductors,  25,000  volts. 

2  7,500  volts  between  conductors  and  sheath. 

8  In  generating  stations  and  substations  to  afford  additional  reliability. 
«  In  generating  stations  to  permit  changing  to  15,000-volt  service. 

5  15,000-volt  service,  same  pressure  to  sheath. 

6  15,000-volt  submarine  section  to  permit  changing  to  23,000  volts. 
*  23,000-volts  half  voltage  to  sheath. 

•  8  23,000-volt  service,  submarine  section. 

9  Includes  3,372  ft.  of  odd  sizes  representing  older  practice. 

10  Specifications  call  for  49  strands  per  conductor,  the  diameters  of  the  individual  strands 
being  largest  at  the  cores  of  the  conductors  and  graded  off  toward  the  outside  to  permit 
flexibility  and  maintenance  of  the  sector  shape.     Tin  is  not  specified  in  the  lead  sheath. 
Break-down  test  between  each  of  two  conductors  and  the  other  two  connected  to  lead  sheath 
of  30,000  volts  for  ft  hr.  (at  factory)  and    23,000  volts  for  10  min.  (after  installation). 
Limits  of  insulation  resistance  in  megohm  miles,  100-400  corrected  to  15.5°C. 

11  Cables  are  designed  for  11,500  volts  to  permit  changing  to  that  pressure  in  the  future. 

12  This  low  rating  has  been  given  because  the  450,000-circ.  mil  cables  are  mixed  in  with 
heavily  loaded  200,000-circ.  mil  cables,  so  it  is  necessary  to  restrict  the  loading  on  the  larger 
ones  to  about  350  amp.  to  prevent  high  temperatures  in  ducts. 

*  Electrical  World,  Feb.  19,  1916. 


CABLES 


129 


based  on  safe  operating  practice  as  predetermined  for  specific 
conditions. 

It  will  be  noted  in  the  foregoing  Table  XXI  that  the  maximum 
voltage  under  which  sector  cable  has  been  operated  is  23,000 
volts  and  considerable  discussion  has  arisen  as  to  the  advis- 
ability of  operating  this  type  of  cable  at  high  voltages,  due  to 
the  excessive  dielectric  stresses  produced  at  the  corners  of  the 
individual  conductors. 

Fig.  58  shows  the  relative  outside  dimensions  of  cables  of 
the  round  and  sector  types,  the  copper  area  and  thickness  of 
insulation  being  the  same  for  each  type. 


of  In 
Inch 


X 


Round 


Type 


100,000 


200,000 


300,000  400,000  500,000  600,000 

Copper  Area  in  Circular  Mils 

FIG.  59. — Increase  in  thickness  of  insulation  possible  by  using  sector 
instead  of  round  conductors,  the  outside  diameter  and  copper  area  being 
the  same  for  each  type.  Insulation  around  conductors  the  same  as  outer 
belt. 

Fig.  59  shows  the  increased  wall  of  insulation  which  can  be 
put  on  a  cable  of  the  sector  type,  the  copper  area  and  outside 
diameter  being  the  same  for  each  type. 

Submarine  Cables. — For  crossing  rivers,  small  lakes,  bays  or 
ponds,  the  beds  of  which  are  mud  or  sand  and  free  from  pebbles, 
stones  or  sharply  defined  channels,  ordinary  lead-covered  cables 
have  been  used,  but  the  addition  of  one  or  two  well-saturated 
stout  braids  has  been  found  advantageous.  If  fiber  or  paper 
insulation  is  used,  it  should  be  thoroughly  saturated  and  filled 
so  as  to  limit  the  damage  in  case  of  injury  to  the  lead  cover,  even 
though  the  cables  be  also  armored  with  steel  tape  or  wires. 

As  a  rule,  however,  and  especially  where  long  lines  of  cables 


130     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

are  to  be  laid  under  water,  it  is  best  to  use  rubber-insulated 
conductors  so  that  in  case  the  protective  covering  should  be 
broken  or  cut,  the  insulation  will  still  exclude  moisture  for  a 
considerable  period  of  time,  if  not  permanently. 

Where  the  submarine  cable  is  at  all  likely  to  be  subjected  to 
considerable  tensile  strains,  the  lead  sheath  should  be  protected 
with  a  heavy  serving  of  tarred  jute,  and  armored  with  galvanized- 
steel  wires  of  a  size  varying  with  the  size  of  the  cable  and  the 
conditions  under  which  the  cable  is  to  be  laid  and  operated. 
Heavily  galvanized  and  pliable  medium-strength  steel  is  used 
for  armor  wire  and  the  size  and  thickness  of  armor  for  various 
diameters  of  cable  is  given  in  the  Standard  Armor  Table  XXII. 

When  the  bottom  on  which  the  cables  lie  is  soft  and  there  is 
no  danger  from  boats  or  dragging  anchors,  paper  cables  with 
extra  heavy  lead,  with  or  without  additional  fibrous  covering 
over  the  lead,  have  been  used  very  successfully. 

It  is  impossible  to  give  instructions  covering  the  installation 
of  submarine  cables  under  all  conditions  but  in  general  the 
following  method  will  be  found  practicable: 

After  procuring  a  tug  or  boat  of  suitable  size  to  carry  the  cable 
reel  and  crew,  the  reel  is  mounted  on  heavy  trusses  at  the  bow 
of  the  boat,  using  a  heavy  shaft  to  support  the  weight  and  allow 
the  reel  to  revolve  readily. 

The  cable  should  pass  from  the  bottom  of  the  reel  over  rollers 
or  pulleys  back  to  the  stern  of  the  boat  and  should  be  securely 
fastened  on  the  shore  at  its  proper  location. 

The  reel  should  be  provided  with  a  brake  so  that  it  will  not 
overrun  as  the  boat  moves,  and  men  should  be  stationed  at  the 
reel  and  cable  roller  to  guard  against  an}r  damage  to  the  cable. 

The  boat  should  move  slowly  to  the  point  where  the  cable  is 
to  land,  and  should  anchor,  or  beach,  bow  on.  The  remainder 
of  the  cable  is  then  unreeled  and  dropped  alongside,  and  the  shore 
end  carried  to  the  point  at  which  it  is  to  meet  the  underground 
or  aerial  line. 

The  shore  end  should  be  laid  in  a  trench  extending  far  enough 
into  the  water  to  protect  the  cable  against  ice  and  boats  which 
may  ground  at  such  points.  In  navigable  waters  a  sign,  "  Cable 
Crossing/'  should  be  prominently  displayed  at  the  cable  landings 
to  prevent  damage  from  boats  inadvertently  anchoring  along 
or  near  the  line  of  the  cable. 

In  the  laying  of  a  submarine  cable  the  boat  should  not  be 


CABLES  131 

TABLE  XXII. — STANDARD  ARMOR  TABLE* 


O.D.  cable,  mils1 

Band  iron 

Wire  armor 

Thickness 

Weight,  Ib. 

Sizes 

Weight,  Ib. 

300 

0.095 

655 

400 

.... 

0.095 

783 

500 

0.030 

748 

0.134 

171 

600 

0.030 

843 

0.134 

1,298 

700 

0.030 

927 

0.134 

1,426 

800 

0.030 

1,020 

0.148 

1,741 

900 

0.030 

1,107 

0.148 

1,891 

1,000 

0.030 

1,198 

0.148 

2,045 

1,200 

0.030 

1,374 

0.148 

2,348 

1,400 

0.030 

1,555 

0.180 

3,202 

1,600 

0.050 

2,454 

0.180 

3,562 

1,800 

0.050 

2,703 

0.180 

3,913 

2,000 

0.050 

2,953 

0.180 

4,265 

2,200 

0.050 

3,202 

0.203 

5,107 

2,400 

0.050 

3,450 

0.203 

5,600 

2,600 

0.050 

3,700 

0.203 

6,100 

*  General  Electric  Co. 

1  Overall  diameter  of  cable  in  mils  before  armor  is  applied. 

NOTE:  For  jute  and  0.030  band  steel   add  0.60  to  diameter. 

For  jute  and  0.050  band  steel  add  0.70  to  diameter. 

For  jute  and  0.095  wire  armor  add  0.60  to  diameter. 

For  jute  and  0.134  wire  armor  add  0.68  to  diameter. 

For  jute  and  0.148  wire  armor  add  0.70  to  diameter. 

For  jute  and  0.180  wire  armor  add  0.80  to  diameter. 

For  jute  and  0.203  wire  armor  add  0.85  to  diameter. 

ARMOR  TABLE 


O.D.  cable,  mils 

10  B.W.G. 

weight 

8  B.W.G. 
weight 

6  B.W.G. 
weight 

4  B.W.G. 
weight 

300 

915 

1,200 

400 

1,050 

1,390 

.... 

.... 

500 

,185 

1,590 

2,100 

.... 

600 

,290 

1,790 

2,400 

2,880 

700 

,430 

1,980 

2,600 

3,250 

800 

,550 

2,180 

2,800 

3,500 

900 

,690 

2,380 

3,000 

3,750 

1,000 

,940 

2,580 

3,300 

4,000 

1,200 

2,200 

2,780 

3,620 

4,500 

1,400 

2,450 

3,180 

4,120 

5,000 

1,600 

2,710 

3,570 

4,500 

5,500 

1,800 

3,040 

3,970 

5,000 

6,000 

2,000 

3,300 

5,500 

6,550 

2,200 

3,550 

5,880 

7,060 

2,400 

3,880 

.... 

6,370 

7,560 

2,600 

4,200 

6,750 

8,060 

allowed  to  drift  with  the  stream  current,  as  a  loop  is  apt  to  be 
formed  in  the  cable  if  a  straight  course  is  not  maintained.     If 


132     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

the  cable  is  allowed  to  slack  off  the  reel  resulting  in  the  forming 
of  a  loop,  there  is  a  possibility  of  creating  a  kink  in  the  cable 
when  the  strain  is  again  put  upon  it. 

Fig.  60  illustrates  the  result  of  a  condition  such  as  just 
described.  This  piece  of  cable  was  cut  from  a  length  of  three- 
conductor,  13,200-volt,  No.  2/0,  paper-insulated,  lead-covered 
and  armored  cable,  and  in  spite  of  this  extraordinary  physical 
abuse  the  cable  continued  to  operate  and  was  still  in  service 
when  the  kink  was  discovered. 

In  a  recent  installation  of  two  submarine  cables  across  the 
Golden  Gate  at  San  Francisco,  a  messenger  wire  was  first  laid 
from  shore  to  shore  and  anchored  securely  at  both  ends. 
This  cable  is  approximately  13,000  ft.  long  and  as  it  could  not 


FIG.  60. — Twisted  submarine  cable. 

be  made  in  one  continuous  length  it  was  necessary  to  make  a 
number  of  splices.  The  messenger,  which  was  a  37-wire  galvan- 
ized-steel  strand  1%  in.  in  diameter,  was  used  to  take  the 
strain,  thus  relieving  the  cable  and  joints  from  all  tension.  In 
laying  the  cable  a  barge  of  125  tons  capacity  was  used,  the  cable 
reels  being  mounted  with  their  axes  parallel  to  the  long  axis  of 
the  barge;  in  this  way  the  barge  was  least  affected  by  the  pre- 
vailing action  of  the  tide  and  waves  in  the  channel.  The  tow  for 
the  cable-laying  equipment  was  a  50-hp.  launch;  during  very 
heavy  tide  runs  two  launches  were  necessary  for  towing  the 
equipment.  When  ready  to  lay  the  cable,  the  messenger  was 
picked  up  at  the  shore  and  laid  across  the  barge.  Two  No.  6 
galvanized  wires  were  wound  around  the  messenger  and  cable. 
These  wires  were  applied  by  a  serving  machine  driven  by  a  gaso- 
line motor.  Every  20  ft.  the  movement  of  the  barge  was  stopped 
by  means  of  a  grip  and  a  considerable  number  of  turns  wound 


CABLES 


133 


around  the  cable  and  the  messenger  at  one  point.  The  speed, 
when  laying  the  cable,  was  about  8  ft.  per  min.  and  when  the 
cable  laying  was  once  started  the  barge  remained  attached  to  the 
messenger  until  the  load  had  been  paid  out. 


&  Tarred  Jute  . 

42  //o.  4  Q.  W£.  Ga/v.  armor  ft  /'res 

^Tarred  jute. 

'Leaof 

"Varnished  c/oth  be/t 
r  Telephone,  joa/r  •  2  //a  /J  D&5.  75trand 
}£Varn/5hedc/ofh,  coffon  brd/'d 


&  Yarn  r  shed  c/of/7  . 

igZubber  3o%Pzra 

250000  c/*.(37t/nned  strands) 


FIG.  61. — Section  of  submarine  power  cable,  11,000  volts  working  pressure. 

The  submarine  cables  (Fig.  61)  are  three-conductor,  250,000- 
cm.  copper,  each  conductor  having  an  insulation  of  %2  m->  30 
per  cent.  Para  rubber  over  which  was  placed  a  ^4-in.  layer  of 


Anchor  Chain 


METHOD  OF  ANCHORING  CABLE  SECTION    C-C 

FIG.  61a. — Details  of  power  cable-anchor,  showing  method  of  taking  the 
strain  on  the  armor  wires. 

varnished  cambric.  The  three  conductors  are  laid  together  in 
circular  form  (a  jute-filler  being  used),  a  1%4-in.  varnished 
cambric  belt  being  applied  over  all.  The  enclosing  sheath  is 
m-  Pure  lead.  Over  the  lead  two  layers  of  jute  are  applied, 


134     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


to  a  total  thickness  of  ^2  m-  The  jute  forms  a  cushion  for  the 
steel-wire  armor,  consisting  of  42  wires  of  No.  4  B.W.G.  extra 
heavy  galvanized  iron  and  this  armor  is  in  turn  covered  with 
a  layer  of  jute  %2  m-  thick,  to  which  was  applied  a  sand  and 
asphaltum  finish  for  mechanical  protection. 

Each  cable  contains  a  twisted  pair  of  telephone  wires  of  No. 
13  B.  &  S.  copper.  Fig.  61a  shows  the  detail  of  the  power-cable 
anchor  and  method  of  taking  the  strain  on  the  armor  wires. 

Specifications.  —  In  submitting  specifications  to  cable  manu- 
facturers, it  is  well  to  state  the  conditions  under  which  the  cable 
will  be  used  as  this  will  assist  the  manufacturer  in  determining 
the  particular  cable  which  will  best  suit  the  operating  conditions. 
When  the  specific  requirements  covering  details  of  construction, 
tests  and  guarantees  of  cable  are  furnished,  a  more  perfect  under- 
standing is  established  and  the  manufacturer  can  better  serve  the 
customer's  needs.  Specifications  are  of  all  classes,  good,  bad  and 
indifferent,  and  taken  collectively,  indicate  a  wide  difference  in 
ideas.  On  the  cable  depends  the  success  of  the  electrical  system 
of  transmission  and  distribution  as  a  poorly  constructed  or 
improperly  insulated  wire  or  cable  will  surely  imperil  the  service. 
The  insulation  should  be  of  the  proper  kind  and  quality  for  the 
purpose  intended.  To  insure  the  service  the  cable  must  be 
properly  tested,  properly  installed  and  properly  protected. 

Gable  should  be  tested  at  the  manufacturer's  plant  before 
shipment,  at  a  potential  somewhat  higher  than  the  maximum 
working  voltage  and  it  is  essential  that  a  similar  test  be  made 
after  installation.  There  still  seems  to  be  a  difference  of  opinion 
as  to  the  proper  pressure  and  duration  of  such  tests  and  there  is 
a  great  tendency  on  the  part  of  engineers  to  make  this  test  too 
severe.  In  general  it  may  be  said  that  tests  of  two  and  one-half 
times  working  pressure  for  30  min.  at  the  factory  and  twice 
the  working  pressure  after  installation  for  15  min.  are  considered 
conservative.  Cables  tested  under  these  conditions  have  given 
no  indication  in  practice  that  the  margin  of  safety  was  not  ample. 
High-potential  tests  are  not  intended  to  show  the  ultimate  strength 
of  the  cable,  but  to  show  that  the  cable  is  safe  and  satisfactory 
for  the  purpose  for  which  it  is  intended. 

In  many  cases  engineers  have  specified  high-puncture  tests  on 
cables  and  it  was  considered  that  if  the  insulation  passed  these 
exacting  tests  it  was  in  first-class  condition.  High-potential 
tests  frequently  strain  the  insulation  to  such  an  extent  that  the 


CABLES  135 

cable  fails  after  the  first  physical  or  potential  strain  is  imposed 
upon  it.  A  high-potential  test  is  not  always  conclusive  proof  of 
insulating  merit,  but  on  the  other  hand  it  should  not  be  assumed 
that  puncture  tests  are  of  no  value.  The  object  of  puncture  tests 
is  to  disclose  imperfections  in  the  insulating  wall  of  the  cable  and 
in  this  respect 'they  are  of  great  importance.  A  cable  may  be 
well  made  of  poor  material  or  it  may  be  imperfectly  made  of  the 
very  best  material.  In  the  one  case  there  is  good  workmanship 
with  poor  material,  and  in  the  other,  bad  workmanship  with 
good  material. 

Cable  specifications  in  general  should  provide  for  the  fixing 
of  the  copper  conditions,  the  insulating  material,  the  sheath  or 
braid  and  the  mechanical,  electrical  and  chemical  tests.  They 
should  include  clauses  providing  for  the  methods  of  tests  and 
apparatus  to  be  used  and,  finally,  instructions  as  to  the  method 
of  packing  and  shipping.  It  should  not  be  the  intent  of  the 
specification  to  tell  the  manufacturer  how  he  shall  make  the  cable. 
The  main  purpose  should  be  to  state  the  operating  conditions 
which  the  cable  must  satisfy  in  order  that  the  manufacturer  may 
endeavor  to  meet  these  conditions. 

Details  of  installation  and  service  may  radically  affect  the 
design  of  any  cable  and  it  is,  therefore,  necessary  that  full  infor- 
mation be  given  the  manufacturer  in  order  to  secure  intelligent 
consideration  and  to  insure  correct  design. 

Rubber-insulated  Cable  Specifications. — The  numerous  speci- 
fications for  30  per  cent,  rubber  compound  do  not  materially 
differ  as  to  chemi  cal  tests,  nor  in  their  requirements  for  mechani- 
cal properties  as  determined  by  stretch,  return,  and  ultimate 
break.  Many  requirements  for  chemical  and  mechanical  prop- 
erties now  found  in  specifications  for  30  per  cent,  compounds 
appeared  originally  in  specifications  for  wires  and  cables  intended 
for  low-tension  service.  The  same  requirements  were  later 
incorporated  in  specifications  for  high-tension  service  and  ac- 
cepted as  satisfactory,  but  experience  has  developed  the  fact  that  a 
change  should  have  been  made  to  secure  the  best  results  for  this 
work.  The  ingredients  of  a  compound  govern  its  characteristics, 
and  a  change  in  the  proportion  of  a  given  ingredient  may  improve 
one  characteristic  to  the  detriment  of  another.  Many  engineers 
leave  the  thickness  of  the  insulation  to  be  determined  by  the 
manufacturer  from  specified  tests.  This  practice  has  the  dis- 
advantage of  permitting  the  various  competing  manufacturers 


136     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

to  submit  their  bids  based  on  different  thicknesses  of  insulation 
and  safety  factors. 

There  are  many  different  grades  of  rubber,  all  varying  in 
price  as  in  quality,  and  it  is  only  by  a  knowledge  and  recognition 
of  this  wide  diversity  of  character  that  an  engineer  can  intelli- 
gently make  up  specifications  and  rigidly  enforce  them.  The 
better  grades  of  rubber  insulation  contain  from  20  to  40  per  cent. 
Para  rubber. 

The  specific  gravity  of  rubber  compounds  varies  from  1.10 
to  2.0  depending  on  the  ingredients  used.  The  higher  the  per 
cent,  of  rubber,  the  lower  the  specific  gravity.  The  tensile 
strength  of  high-grade  rubber  compound  is  about  1,200  Ib.  per 
sq.  in. 

Rubber  insulation,  owing  to  its  composition,  attacks  copper  and 
it  is,  therefore,  necessary  that  the  conductor  be  properly  tinned 
before  the  insulation  is  applied.  In  testing  rubber-covered 
cables  it  is  customary  to  apply  the  potential  test  at  the  factory 
while  the  cables  are  immersed  in  testing  tanks  in  which  the  water 
is  maintained  at  a  constant  temperature.  These  tests  are  made 
when  the  conductor  is  covered  with  the  vulcanized  compound 
and  before  the  application  of  any  covering  other  than  a  non- 
waterproof  tape.  The  analysis  of  rubber  compounds  presents 
extraordinary  difficulties  and  in  the  present  state  of  the  art  no 
one  procedure  is  applicable  to  all  compounds.  Serious  difficul- 
ties have  arisen  in  the  past,  due  to  the  want  of  standard  methods. 
For  several  years  no  attempt  was  made  to  standardize  specifica- 
tions, and  much  trouble  was  given  the  manufacturers  by  the  di- 
versity  of  requirements  contained  in  the  various  specifications. 
In  1911,  Mr.  E.  B.  Katte,  chief  engineer  of  electric  traction 
of  the  New  York  Central  and  Hudson  River  Railroad  Co., 
invited  a  number  of  manufacturers  and  consumers  to  a  confer- 
ence in  order  to  discuss  the  possibility  of  standardizing  specifica- 
tions and  analytical  methods  for  rubber  insulation.  As  a  result 
of  this  conference  which  was  held  in  New  York  on  Dec.  7,  1911,  a 
committee  was  appointed  to  devise  a  specification  and  analytical 
procedure  for  rubber  insulation.  The  committee,  which  has 
become  known  as  the  Joint  Rubber  Insulation  Committee,  was 
composed  of  men  representing  the  various  interests,  and  a  report 
was  submitted  on  the  procedure  for  chemical  analysis  and  the 
interpretation  of  the  results  obtained.  A  specification  and  chem- 
ical limits  for  a  30  per  cent,  compound  was  also  included. 


CABLES  137 

The  procedure  applies  only  to  a  limited  class  of  compounds 
and  is  not  ordinarily  applicable  to  compounds  containing  less 
than  30  per  cent,  of  rubber.  The  committee  report  is  printed 
in  full  in  the  Proceedings  of  the  American  Institute  of  Electrical 
Engineers,  vol.  33,  1914. 

The  following  specification  for  30  per  cent,  rubber  insulating 
compound  is  submitted  for  lead-sheathed  cables  for  operating 
at  pressure  in  excess  of  2,000  volts.  The  general  clauses  cover- 
ing conductors,  sheaths,  patents,  quantities,  shipments,  reels, 
terms  of  payment,  permits,  measurements,  etc.,  as  given  under 
the  heading  of  paper-insulated  cable  specification,  will  also  apply 
for  rubber  cable  specifications. 

SPECIFICATION  FOB  RUBBER-INSULATED  CABLES 

1.  Conductors  shall  be  properly  tinned. 

2.  The  insulating  compound  shall  be  made  exclusively  from  pure,  dry, 
raw,  wild  South  American  Para  rubber,  of  best  quality  of  the  grade  known 
as  "fine,"  solid  waxy  hydrocarbons,  suitable  mineral  matter  and  sulphur. 

3.  It  shall  be  properly  and  thoroughly  vulcanized. 

4.  The  vulcanized  compound  shall  show  on  analysis,  freedom  from  all 
foreign  organic  or  injurious  mineral  matter;  not  less  than  30  nor  more  than 
33  per  cent,  of  above-specified  rubber;  not  more  than  4  per  cent,  of  solid 
waxy  hydrocarbons;  not  more  than  1.5  per  cent,  of  rubber  resins;  not  more 
than  0.7  per  cent,  of  free  sulphur  and  not  more  than  2.65  per  cent,  of  total 
sulphur  in  any  form. 

5.  The  manufacturer  shall  submit  to  the  company  a  method  of  procedure 
for  chemical  analysis  of  his  compound  for  the  guidance  of  the  company's 
chemist  in  order  that  intelligent  comparisons  may  be  made  in  the  event  of 
dispute  between  the  manufacturer  and  company. 

6.  The  compound  must  be  homogeneous  hi  character,  tough,  elastic, 
adhere  strongly  to,  and  be  placed  concentrically  about  the  wire,  and  in 
section  as  stripped  from  the  wire  must  have  a  specific  gravity  of  not  less  than 
1.75  as  compared  with  distilled  water  at  60°F. 

7.  A  sample  of  the  vulcanized  compound  not  less  than  4  in.  in  length 
and  of  uniform  cross-section  shall  be  cut  from  the  wire  and  marks  placed  on 
it  2  in.  apart.     The  sample  shall  be  stretched  longitudinally  at  the  rate  of  12 
in.  per  min.  until  the  marks  are  6  in.  apart  and  then  immediately  released. 
One  minute  after  such  release  the  marks  shall  not  be  over  2^  in.  apart. 
The  sample  shall  then  be  stretched  until  the  marks  are  10  in.  apart  before 
breaking. 

8.  The  compound  shall  have  a  tensile  strength  of  not  less  than  1,000  Ib. 
per  sq.  in.,  based  on  the  original  cross-section  of  the  test  piece  before  stretch. 

9.  The  above  mechanical  tests  shall  be  made  at  a  temperature  of  not 
less  than  50°F. 

10.  Each  and  every  length  of  conductor  shall  comply  with  the  mechanical 


138     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

and  electrical  requirements  indicated  in  the  following  tables  "A"  and  "B." 
The  tests  at  the  works  of  the  manufacturer  shall  be  made  when  the  con- 
ductor is  covered  with  the  vulcanized  compound  and  before  the  application 
of  any  covering  other  than  a  non-waterproof  tape. 

11.  Electrical  tests  at  the  factory  on  single-conductor  cables  shall  be 
made  after  at  least  12  hr.  submersion  in  water  and  while  still  immersed. 
The  insulation  test  shall  follow  the  voltage  test  and  shall  be  made  with  a 
battery  of  not  less  than  100  volts  or  more  than  500  volts  and  the  reading 
shall  be  taken  after  1  min.  electrification. 


TABLE  "A" 

Voltage  tests  on  single-conductor  cables  insulated  with  high-tension  rubber 
compound.  Duration  of  test  at  factory  5  min.;  after  installation,  30  min. 
Tests  at  factory  as  per  table;  after  installation  at  table  values  for  5  min.,  then 
at  80  per  cent,  for  25  min. 


Size  conductor 

Minimum  thickness  of  insulation  in  inches 

3/32 

7/64 

4/32 

5/32 

6/32 

7/32 

8/32 

14/32 

Stranded 
1,000  M.C.M  

6,000 
6,000 
7,000 
7,000 
8,000 
8,000 
8,000 
9,000 

9,000 
9,000 
9,000 
9,000 
9,000 
9,000 

8,000 
8,000 
9,000 
9,000 
10,000 
10,000 
10,000 
11,000 

11,000 
11,000 
10,000 
10,000 
10,000 
10,000 

12,000 
12,000 
13,000 
13,000 
13,000 
13,000 
13,000 
14,000 

14,000 
14,000 
11,000 
11,000 
11,000 
11,000 

16,000 
16,000 
16,000 
16,000 
16,000 
16,000 
16,000 
16,000 

16,000 
16,000 
12,000 
12,000 
12,000 
12,000 

19,000 
19,000 
19,000 
19,000 
19,000 
19,000 
19,000 
18,000 

18,000 
18,000 

22,000 
22,000 
22,000 
22,000 
22,000 
22,000 
22,000 
20,000 

20,000 
20,000 

30,000 
30,000 
30,000 
30,000 
30,000 
30,000 
30,000 
30,000 

30,000 
30,000 

750  M.C.M  

500  M.C.M  
350  M.C.M  
4/0  A  W  G 

5,000 
5,000 
6,000 
6,000 
6,000 
7,000 

7,000 
7,000 
7,500 
7,500 
7,500 
7,500 

2/0  A.W.G  
1/0  A  W  G 

2  A  WG 

Solid 
4  A.W.G  
6  A.W.G.      .   . 

8  A.W.G  
10  A  WG 

12  A.W.G  
14  A.W.G  



13.  Samples  of  the  cables  6  ft.  in  length  taken  from  any  reel  of  cable 
must  show  an  ultimate  dielectric  strength  capable  of  resisting  the  applica- 
tion of  twice  the  voltage  specified  above  for  a  period  of  5  min.  without 
failure. 

14.  Insulation  resistance  and  electrostatic  capacity  tests  made  (before 
and  after  voltage  tests  as  per  Table  "A")  and  under  equivalent  temperature 
conditions  must  not  indicate  fatigue  or  overstrain  of  dielectric. 


CABLES 


139 


15. 


TABLE  "B" 


Insulation  tests  on  single-conductor  cables  insulated  with  high-tension 
rubber  compound.  Tests  at  factory  as  per  table;  after  installation  80  per  cent, 
of  table  value. 

MINIMUM  MEGOHMS  PER  MILE  AT  60°F. 


Size  conductor 

Minimum  thickness  of  insulation  in  inches 

5/64 

3/32 

7/64 

4/32 

5/32 

6/32 

7/32 

8/32 

14/32 

Stranded 
1,000  M  C  M 

300 
350 
410 
520 
610 
740 
800 
1,070 

1,260 
1,480 
1,720 
1,990 
2,270 
2,560 

340 
400 
460 
580 
680 
820 
980 
1,170 

1,380 
1,610 
1,870 
2,150 
2,440 
2,740 

420 
490 
570 
700 
820 
980 
1,060 
1,380 

1,610 
1,860 
2,140 
2,440 
2,750 
3,060 

490 
570 
660 
810 
940 
1,130 
1,210 
1,560 

1,800 
2,070 
2,360 
2,680 
3,000 
3,320 

560 
650 
750 
910 
1,060 
1,260 
1,350 
1,720 

1,980 
2,260 
2,570 
2,890 
3,220 
3,550 

630 
730 
830 
1,010 
1,170 
1,380 
1,470 
1,870 

2,140 
2,430 
2,750 
3,000 
3,420 
3,750 



750  M  C  M 

500  M  C  M 

350  M  C  M 

4/0  A  W  G 

530 
650 
710 
950 

1,130 
1,330 
1,560 
1,810 
2,080 
2,360 

2,000 
2,240 
2,400 
2,750 

3,200 
3,600 

2/0  A  W  G 

1/0  A  W  G 

2  A.W.G.... 
Solid 
4  A.W.G.... 
6  A.W.G.... 
8  A  W  G 



10  A.W.G.... 
12  A.W.G.... 
14  A.W.G.... 



1,860 
2,120 

SPECIFICATIONS 
FOR 

PAPER-INSULATED, 
LEAD-ENCASED  CABLES 

FOR 

ELECTRIC-LIGHTING,  RAILWAY  AND  POWER  SERVICE 


1.  GENERAL 

(a)  The  word  "Company"  where  occurring  in  these  specifications  shall 
mean  the  purchaser  »f  the  cable  herein  referred  to,  or  its  duly  authorized 
representative. 

(6)  The  word  "Manufacturer"  where  occurring  in  these  specifications 
shall  mean  the  manufacturer  of  the  cable  herein  referred  to,  or  his  duly 
authorized  representative. 

2.  RATING  OP  CABLE 

(a)  The  rating  of  a  cable  shall  be  understood  to  be  the  highest  equivalent 
working  pressure  in  volts  corresponding  to  any  of  the  specified  conditions 
of  service  or  test.  Such  rating  shall  be  determined  from  the  following 


140     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

Rating  Table  XXIII,  all  unlisted  intermediates  taking  the  next  higher  listed 
figure. 

TABLE  XXIII. — VOLTAGE  RATING  OP  CABLES 


Working 
pressure 
volts 

rr>  4.  4.  t  4.     IA          Test  after  installation  by  manufac- 
Test  at  factory,  volts                 turer>  voits  * 

5  min. 

30  min. 

60  min. 

5  min. 

30  min. 

60  min. 

500 
1,000 
1,500 

1,250      1,000 
2,500      2,000 
3,750      3,000 

1,000      1,000 
1,600      2,000 
2,400      3,000 

1,000      1,000 
1,600      1,300 
2,400      1,950 

2,000 
2,500 
3,000 

5,000 
6,250 
7,500 

4,000 
5,000 
6,000 

3,200      4,000 
4,000      5,000 
4,800      6,000 

3,200      2,600 
4,000      3,250 
4,800      3,900 

4,000 
5,000 
6,000 

10,000      8,000 
12,500     10,000 
15,000     12,000 

6,400      8,000 
8,000      10,000 
9,600      12,000 

6,400      5,200 
8,000      6,500 
9,600      7,800 

7,000 
8,000 
9,000 

17,500     14,000 
20,000     16,000 
22,500     18,000 

11,200      14,000 
12,800      16,000 
14,400      18,000 

11,200 
12,800 
14,400 

9,100 
10,400 
11,700 

10,000 
11,000 
12,000 

25,000     20,000 
27,500      22,000 
30,000      24,000 

16,000      20,000 
17,600      22,000 
19,200  •     24,000 

16,000 
17,600 
19,200 

13,000 
14,300 
15,600 

13,000 
14,000 
15,000 

16,000 
17,000 
18,000 

32,500 
35,000 
37,500 

40,000 
42,500 
45,000 

26,000 
28,000 
30,000 

32,000 
34,000 
36,000 

20,800 
22,400 
24,000 

25,600 
27,200 
28,800 

26,000 
28,000 
30,000 

32,000 
34,000 
36,000 

20,800 
22,400 
24,000 

25,600 
27,200 
28,800 

16,900 
18,200 
19,500 

20,800 
22,100 
23,400 

19,000 
20,000 
21,000 

47,500 
50,000 
52,500 

38,000 
40,000 
42,000 

30,400 
32,000 
33,600 

38,000 
40,000 
42,000 

30,400 
32,000 
33,600 

24,700 
26,000 
27,300 

22,000 
23,000 
24,000 

55,000 
57,500 
60,000 

44,000 
46,000 
48,000 

35,200 
36,800 
38,400 

44,000 
46,000 
48,000 

35,200 
36,800 
38,400 

28,600 
29,900 
31,200 

25,000 
26,000 
27,000 

62,500 
65,000 
67,500 

50,000 
52,000 
54,000 

40,000 
41,600 
43,200 

50,000 
52,000 
54,000 

40,000 
41,600 
.  43,200 

32,500 
33,800 
35,100 

28,000 
29,000 
30,000 

70,000 
72,500 
75,000 

56,000 
58,000 
60,000 

44,800 
46,400 
48,000 

56,000 
58,000 
60,000 

44,800 
46,400 
48,000 

36,400 
37,700 
39,000 

Factors..  .  .    2.5 

2.0 

1.6       2.0 

1.6 

1.3 

For  street  railway  service  (nominal  500-volt  d.c.),  the  e.w.p.  shall  be  2,500  volts  for  all 
cables  to  be  operated  with  a  maximum  regular  working  voltage  not  exceeding  750  volts 
d.c.  and  a  maximum  momentary  pressure  (30  sec.  or  less  )  not  exceeding  1,500  volts  d.c. 

(6)  For  street-railway  service  nominal  600  volts  d.c.,  the   equivalent 


CABLES  141 

working  pressure  shall  be  2,500  volts  for  all  cables  to  be  operated  with  a 
maximum  regular  working  voltage  not  exceeding  750  volts  d.c.,  and  a 
maximum  momentary  pressure  (30  sec.  or  less)  not  exceeding  1,500  volts  d.c. 
(c)  For  three-conductor  three-phase  "Y  "-connected  circuits  with 
grounded  neutral,  the  thickness  of  insulation  between  any  conductor  and 
ground  need  be  only  seven-tenths  of  that  between  conductors,  and  the  test 
voltage  between  any  conductor  and  ground  may  be  taken  at  seven-tenths 
of  the  above  tabulated  figures  for  the  corresponding  equivalent  working 
pressure. 

3.  CONDUCTOKS 

(a)  Each  conductor  shall  consist  of  not  less  than  the  following  number 
of  soft-drawn  copper  wires  free  from  splints,  flaws,  joints,  or  defects  of  any 
kind,  and  having  at  least  98  per  cent,  conductivity  of  that  of  pure  annealed 
copper,  as  defined  by  the  American  Institute  of  Electrical  Engineers 
Standardization  Rules.  The  conductors  shall  be  concentrically  stranded 
together  having  an  aggregate  cross-sectional  area  when  measured  at  right 
angles  to  the  axes  of  the  individual  wires  at  least  equal  to  that  corresponding 
to  the  specified  size,  viz: 

No.  4  B.  &  S.  G and  smaller Solid 

No.  3  B.  &  S.  G to  No.  2  B.  &  S.  G. . .     7-wire  strand 

No.  1  B.  &  S.  G to  No.  4/0  B.  &  S.  G. .   19-wire  strand 

250,000  cm to  500,000  cm 37-wire  strand 

600,000  cm to  1,000,000  cm 61-wire  strand 

1,100,000  cm to  2,000,000  cm 97-wire  strand 

2,100,000  cm and  larger 127-wire  strand 

Intermediate  sizes  take  the  stranding  of  the  next  larger  listed  size. 

4.  INSULATION 

(a)  The  insulation  shall  consist  of  the  best  manila  paper  free  from  jute, 
wood  fiber  or  other  foreign  material  applied  helically  and  evenly  on  the  con- 
ductor, and  shall  be  capable  of  withstanding  the  test  and  service  conditions 
corresponding  to  the  highest  equivalent  working  pressure  as  determined  from 
the  rating  table  set  forth  hi  paragraph  2  hereof.  In  the  case  of  the  cables 
consisting  of  more  than  one  conductor  (except  concentric  cables)  and  Fig. 
8  or  flat  form  of  duplex  cables,  the  separately  insulated  conductors  shall  be 
twisted  together  with  a  suitable  lay,  and  interstices  rounded  out  with  the 
jute'  before  the  belt  insulation  is  applied.  The  minimum  insulation  thick- 
ness or  thicknesses  shall  in  no  case  be  less  than  90  per  cent,  of  the  agreed 
average  thickness  or  thicknesses.  The  completed  core  shall  be  thoroughly 
insulated  with  an  insulating  compound. 

5.  SHEATH 

(a)  The  sheath  shall  have  an  average  thickness  of  not  less  than  that 
indicated  in  the  tabulation  next  following  and  the  minimum  thickness 
shall  in  no  case  be  less  than  90  per  cent,  of  the  required  average  thickness. 


142     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

Diameter  of  core  Corresponding  thickness 

in  mils  of  sheath  in  inches 

0-299  5/64 

300-699  3/32 

700-1,249  7/64 

1,250-1,999  1/8 

2,000-2,699  9/64 

2,700-over  5/  32 

(b)  The  sheath  shall  consist  of  commercially  pure  lead,  freshly  mined 
and  shall  contain  no  scrap,  and  shall  be  free  from  blow  holes,  cracks,  scales 
or  imperfections  of  any  kind. 

6.  FACTORY  TESTS 

(a)  The  manufacturer  shall,  when  so  stipulated  in  the  order,  notify  the 
company  in  writing  when  the  cables  are  ready  for  test,  so  that  proper  tests 
may  be  made  at  the  works  of  the  manufacturer  by  the  duly  accredited  repre- 
sentative of  the  company.     Free  access  to  the  testing  department  shall  be 
given  to  said  representative  at  all  times  while  the  cables  are  being  tested 
hereunder,  and  the  requisite  facilities  and  apparatus  for  the  tests  described 
in  these  specifications  shall  be  supplied  by  the  manufacturer  without  extra 
charge.     In  case  the  representative  appointed  by  the  company  to  make 
factory  tests  is  not  wholly  and  permanently  in  the  employ  of  the  company, 
said  appointment  shall  be  subject  to  the  approval  of  the  manufacturer. 

(b)  Conductivity. — The  conductivity  of  the  copper  shall  be  determined 
at  least  once  for  each  day's  output. 

(c)  Dielectric  Strength. — Each  length  of  cable  shall  withstand  tests  at 
factory   of   a  voltage   corresponding   to   the   rating    (highest   equivalent 
working  pressure)  of  the  cable  as  determined  from  the  rating  table.     The 
condition  and  conduct  of  test  shall  conform  to  the  Standardization  Rules 
of  the  American  Institute  of  Electrical  Engineers. 

(d)  Insulation   Resistance. — The  insulation   resistance   shall   be    deter- 
mined on  each  length  of  cable  and  shall  not  be  less  than  50  megohms  when 
measured  at,  or  corrected  to,  60°F.     This  test  shall  be  made  subsequent  to 
the  tests  for  dielectric  strength.     (Higher  insulation  resistance  can  be  fur- 
nished, but  necessitates  the  use  of  a  harder  insulating  compound,  which  is 
more  inclined  to  dry  out  and  cannot  safely  be  bent  in  cold  weather.) 

(e)  Testing  Apparatus  and  Methods. — Any  disagreement  as  to  the  accuracy 
of  testing  apparatus  or  method  not  specifically  covered  by  this  specification 
shall  be  referred  to  the  Bureau  of  Standards,  Washington,  D.  C. 

7.  PATENTS 

(a)  The  manufacturer,  shall,  at  his  own  expense,  defend  any  or  all  suits 
or  proceedings  that  may  be  instituted  against  the  company  for  the  in- 
fringement or  alleged  infringement  of  any  patent  or  patents,  by  the  use  of 
any  cable  or  goods  covered  by  this  specification,  and  sold  to  the  company 
by  the  manufacturer  provided  such  infringement  shall  consist  in  the  use  by 
the  company,  in  the  regular  course  of  its  business,  of  any  of  said  cable  or 


CABLES  143 

goods  or  parts  thereof,  and  provided  the  company  gives  to  the  manufacturer 
immediate  notice  in  writing,  of  the  institution  of  the  suit,  or  proceedings, 
and  permits  the  manufacturer  through  his  counsel,  to  defend  the  same  and 
gives  all  needed  information,  assistance,  and  authority  to  enable  the  manu- 
facturer so  to  do,  and  thereupon,  in  case  of  an  award  of  the  damages,  the 
manufacturer  shall  pay  such  award  and  in  case  of  an  injunction  against  the 
company,  the  manufacturer  shall,  upon  return  of  the  article,  the  use  of 
which  has  been  enjoined,  repay  to  the  company  the  amount  paid  by  it  for 
the  same. 

8.  QUANTITIES 

(a)  The  quantity  of  each  cable  specified  in  the  order  shall  be  subject 
to  an  increase  or  decrease  of  not  exceeding  5  per  cent.,  at  the  option  of  the 
company,  provided  that  such  option  is  exercised  by  the  company  in  writing 
not  less  than  30  days  before  the  date  fixed  for  final  shipment  on  account  of 
said  order. 

9.  SHIPMENTS 

(a)  Unless  otherwise  provided  all  deliveries  shall  be  f.o.b.  factory  of  the 
manufacturer.  Any  material  not  called  for  by  the  company  in  time  to 
permit  the  manufacturer  (at  the  agreed  shipping  rates)  to  make  shipment 
within  the  agreed  time,  and  for  which  final  shipping  instructions  are  not 
filed  by  the  company  with  the  manufacturer  at  least  1  month  prior  to  the 
expiration  of  said  agreed  time,  shall  be  paid  for  as  if  shipped  at  the  expiration 
of  said  agreed  time.  Provided,  however,  that  said  agreed  time  shall  not  be 
more  than  6  months  after  date  of  order.  A  receipt  given  by  the  company 
or  its  representatives  for  any  material  .shipped  by  the  manufacturer,  and 
which  fails  to  note  any  apparent  injury  to  or  bad  condition  of  reels,  cases  or 
contents  shall  terminate  the  manufacturer's  responsibility  for  the  condition 
of  said  material. 

10.  REELS 

(a)  All  reels  and  lagging  shall  not  be  included  in  the  contract  price,  but 
shall  be  charged  separately  therefrom  and  shall  be  paid  for  in  accordance 
with  paragraph  11  thereof,  "Terms  of  Payment,"  and  when  returned  f.o.b 
shipping  factory  in  good  condition  complete  with  all  lagging  (reasonable 
wear  and  tear  excepted)  within  6  months  from  date  of  shipment  shall  be 
credited  at  the  price  charged.  Reels  and  lagging  thus  returned  after  6 
months  from  date  of  shipment  shall  be  credited  at  one-half  the  price  originally 
charged. 

(6)  Each  reel  shall  be  plainly  marked,  giving  the  length  of  cable,  pur- 
chaser's order  number,  and  date  of  manufacture.  Each  reel  shall  have  a 
numbered  metal  tag,  permanently  attached. 


11.  TERMS  OF  PAYMENT 

(a)  Net  cash  within  30  days  from  date  of  payment  by  manufacturer;  or 
per  cent,  discount  for  cash  within  10  days  from  said  date  of  shipment. 


144     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

12.  INSTALLATION  BY  MANUFACTURER 

(a)  The  following  additional  conditions  contained  in  paragraphs  12  to 
22,  both  inclusive,  hereof  shall  apply  when  cable  is  installed  in  underground 
ducts  and  manholes  by  the  manufacturer,  and  then  only;  in  which  case  the 
conditions  of  paragraphs  10  and  11  hereof  shall  be  cancelled. 

13.  PERMITS  AND  INFORMATION 

(a)  The  company  shall  provide  all  necessary  permits  and  information 
to  enable  the  manufacturer  to  carry  on  the  work  uninterruptedly. 

14.  MEASUREMENTS 

(a)  The  company  shall  furnish  the  manufacturer  correct  measurements 
for  detail  manufacturing  lengths,  but  in  case  the  company  so  elects  at  the 
time  of  placing  the  order,  the  manufacturer  shall  make  said  measurements, 
which  shall  be  approved  by  the  company  before  the  manufacture  of  the 
cable  is  begun.  In  either  case  the  lengths  as  thus  determined  shall  be  paid 
for  under  paragraph  21  hereof,  relating  to  "payments,"  and  the  scrap  or 
excess  cable,  if  any,  shall  become  the  property  of  the  company. 

15.  CONDUITS,  MANHOLES,  ETC. 

(a)  All  conduits,  manholes,  or  locations  provided  by  the  company  for 
the  reception  of  cable  shall  be  clean  and  free  from  obstructions,  safe  and 
suitable  for  the  purpose  intended.  The  ducts  shall  be  such  as  to  permit  the 
passing  through  them  of  a  steel  mandrel,  3  ft.  in  length  and  of  a  diameter  at 
least  %  in.  greater  than  that  of  the  cable  to  be  installed  therein,  but  in  no 
case  of  a  smaller  diameter  than  Y±  in.  less  than  that  of  the  nominal  diameter 
of  the  ducts;  in  case  obstructions  or  defects  in  the  ducts  assigned  by  the 
company  cause  unavoidable  delay  to  the  manufacturer  or  damage  to  cable 
through  attempts  to  install  therein,  the  company  shall  pay  to  the  manu- 
facturer the  actual  loss  resulting  from  said  delay,  and  cost  of  repairing  said 
damage. 

16.  JOINTING 

(a)  The  manufacturer  shall  make  all  joints  in  a  substantial  and  work- 
manlike manner,  using  proper  connectors  of  the  proper  conductivity,  which 
shall  be  sweated  to  the  conductor  so  as  to  furnish  perfect  continuity  at  all 
points.  Sufficient  insulating  material  shall  be  supplied  to  insure  insulation 
and  dielectric  strength  equal  to  the  average  obtained  to  equal  lengths  of  the 
cable  as  manufactured.  The  joints  shall  be  provided  with  lead  sleeves  of 
thickness  not  less  than  that  of  the  sheath  of  the  cable;  they  shall  be  thor- 
oughly made,  wiped,  and  filled  with  compound  to  prevent  the  probability 
of  moisture,  reaching  the  insulation. 


CABLES  145 

17.  INSTALLED  TEST 

(a)  After  the  cable  is  pulled  in  and  jointed  by  the  manufacturer,  and 
before  being  put  into  service,  it  shall  be  subjected  to  an  installed  test  at  a 
voltage  corresponding  to  the  rating  or  highest  equivalent  working  pressure 
of  the  cable  as  determined  from  the  rating  table  set  forth  in  paragraph  2 
hereof.  Unless  otherwise  specified  by  the  company  in  writing  at  or  prior 
to  time  of  test,  the  latter  shall  be  the  listed  test  for  5  min.  set  forth  in  said 
rating  table.  The  necessary  current  and  apparatus  for  making  the  test 
shall  be  supplied  by  the  company,  the  conditions  and  conduct  of  tests  shall 
conform  to  the  recommendation  of  the  Standardization  Rules  of  the  Ameri- 
can Institute  of  Electrical  Engineers. 


18.  TERMINALS  AND  JUNCTION  BOXES 

(a)  Terminals,  junction  boxes,  manhole  cable  supports  and  in  general 
all  cable  accessories  or  auxiliary  apparatus  not  necessarily  required  to  be 
used  in  connection  with  the  pulling  in  and  jointing  of  the  cable,  shall  be 
provided  by  the  company. 

(6)  If  so  instructed  by  the  company,  the  manufacturer  shall  make  con- 
nection between  the  cable  and  terminals,  junction  boxes,  or  equivalent,  but 
shall  not  be  required  to  guarantee  the  same  hereunder  unless  said  terminals 
and  junction  boxes  or  equivalent  are  approved  by  him. 

(c)  In  any  estimate  or  count  of  the  number  of  joints  the  following  under- 
standing shall  apply: 

Each  straight  joint  counts  as  one  joint. 

Each  additional  branch  or  tap  cable  from  a  straight  joint  counts  as  one 
joint. 

Each  cable  entering  or  leaving  a  junction  box,  test  box,  terminal,  pothead 
or  equivalent,  counts  as  one  joint. 

19.  GUARANTEE 

(a)  In  case  any  cable  furnished  hereunder  fails  within  1  year  from  date  of 
shipment  by  the  manufacturer,  and  said  failure  results  from  defects  of 
material  or  workmanship  for  which  the  manufacturer  is  shown  to  be  solely 
responsible,  the  manufacturer  shall  be  immediately  notified  and  shall 
(being  given  suflficient  time  to  enable  him  to  do  so)  at  his  own  expense  make 
all  necessary  repairs  to  make  the  cable  affected,  in  every  way  equal  to  its 
condition  previous  to  its  failure. 

(6)  Should  the  manufacturer  fail  to  attend  to  the  repairs  promptly,  or 
should  the  exigencies  of  the  company's  business  be  such  as  to  necessitate 
repairs  before  the  manufacturer  can  be  notified,  the  company  shall  have  the 
right  to  make  the  necessary  repairs  at  the  manufacturer's  expense,  preserving 
the  available  evidence  of  the  cause  of  the  failure. 

(c)  Should  the  evidence  fail  to  show  the  liability  of  the  manufacturer 
under  this  specification,  the  company  shall  pay  to  the  manufacturer  the 
cost  of  repairs  made  by  the  latter. 


10 


146     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


20.  ACCIDENT  LIABILITY 

(a)  The  manufacturer  shall  save  the  company  free  and  harmless  from 
any  and  all  claims  or  demands  of  the  manufacturer's  employees  or  his 
legal  representatives  for  injury  which  may  be  substained  while  employed 
in  the  construction  of  the  work  herein  contemplated,  or  while  going  to  or 
from  the  place  where  said  work  is  to  be  performed,  unless  such  injury  is 
due  to  negligence  on  the  part  of  the  company  or  its  employees;  also  from 
any  and  all  claims  or  demands  for  damages,  for  injury  to  other  parties, 
caused  by  the  fault  or  neglect  of  the  manufacturer,  his  agents,  servants,  01 
employees  in  the  construction  of  said  improvements. 

(6)  Provided  that  in  the  event  of  any  action  or  actions  which  may  be 
instituted  either  by  the  agent,  servants,  or  employees  of  the  manufacturer 
against  the  company,  or  by  third  persons  who  may  claim  injuries  to  have 
been  sustained,  within  the  meaning  of  the  foregoing  clause  (which  injuries 
are  alleged  to  be  the  result  of  the  fault  or  neglect  of  the  agents,  employees, 
or  servants  of  the  manufacturer),  the  company  shall  immediately  notify  the 
said  manufacturer  thereof,  and  shall  permit  him  to  institute  suit  or  action 
and  appear  and  participate  in  the  trial  by  counsel  of  his  own  selection. 
Provided,  further,  however,  that  this  proviso  shall  not  in  anywise  prevent 
the  said  company  from  defending  against  suit  or  action  with  as  full  force 
and  effect  as  though  the  preceding  paragraph  in  the  said  contract,  to  which 
this  is  a  proviso,  had  not  been  inserted  in  contract. 

21.  TERMS  OF  PAYMENT 

(a)  Net  cash  for  80  per  cent,  of  the  installed  price  shall  be  paid  within 
30  days  from  date  of  shipment.  Ten  per  cent,  of  the  installed  price  (one- 
half  of  the  remaining  20  per  cent.)  shall  be  paid  upon  the  tenth  day  of  each 
calendar  month  for  all  cable  pulled  in  and  jointed  during  the  preceding 
calendar  month,  and  the  remaining  10  per  cent,  due  for  each  separate  cable, 
shall  be  paid  within  10  days  from  the  date  when  each  such  cable  shall  have 
been  tested  and  accepted  such  test  and  final  acceptance  or  rejection  of  each 
separate  cable  to  be  made  within  10  days  from  notice  by  the  manufacturer 
to  the  company  that  such  cable  is  ready  for  final  test.  If  the  installation 
of  any  cable  or  part  thereof  be  delayed  for  more  than  3  months  by  failure 
or  inability  of  the  company  to  provide  the  manufacturer  with  the  necessary 
facilities  for  prosecuting  the  installation,  or  by  other  causes  not  attributable 
to  the  manufacturer,  the  full  balance  remaining  unpaid  for  such  cable 
(taking  into  consideration  the  due  proportion  of  installation  work  done  upon 
the  cable,  if  any),  also  the  unpaid  balance  for  all  cable  accessories  furnished 
in  connection  therewith  and  the  manufacturer's  customary  charge  for  the 
reels  thus  retained  by  the  company,  shall  be  due  and  shall  be  paid  forthwith. 

High-tension  Cable  Specification. — The  National  Electric 
Light  Association  Committee  on  Underground  Construction 
suggest  the  following  specification  for  three-conductor  paper- 
insulated  cable.  It  will  be  noted  that  in  this  specification  a 


CABLES  147 

bending  test  is  included.  In  European  cables  the  bending  test 
is  applied  three  times  to  a  radius  of  six  times  the  cable  diameter. 
American  manufacturers  consider  as  too  severe  a  bending  test, 
first  in  one  direction  and  then  in  the  other,  twice  repeated,  to  a 
radius  of  six  times  the  cable  diameter.  The  specification  here- 
with presented,  therefore,  increases  the  radius  of  bending  to  seven 
and  one-half  times  the  cable  diameter. 

INSULATING  MATERIAL 

The  insulating  material  shall  be  of  the  best  manila  paper, 
free  from  jute,  wood  fiber,  or  other  foreign  material.  It  shall  be 
cut  in  strips  and  helically  and  evenly  applied  to  the  conductor 

to  a  uniform  thickness  of /32  in.  After  insulation  the  three 

conductors  shall  be  laid  together,  with  a  uniform  twist,  having 
a  pitch  not  exceeding  25  times  the  diameter  of  one  conductor 
measured  over  the  insulation.  The  interstices  shall  be  filled  with 
jute  or  paper  so  as  to  form  a  true  firm  cylinder  without  openings 
or  air  spaces,  over  which  is  to  be  applied  a  paper-insulating 
jacket  in  the  same  manner,  and  of  the  same  quality  as  specified 
for  each  conductor. 

During  the  process  of  applying  the  paper  insulation  and  the 
jute  or  paper  filler  and  immediately  before  the  insulation  is 
impregnated,  the  cable  shall  be  subjected  to  such  treatment  as 
will  insure  the  expulsion  of  all  air  and  moisture,  incident  to 
which  treatment  the  cable  shall  be  impregnated  with  an  insulat- 
ing compound  of  low  specific  inductive  capacity,  guaranteed  not 
to  run  appreciably  and  to  retain  its  sticky  adhesive  qualities 
during  the  life  of  the  cable,  and  also  guaranteed  not  to  develop 
any  chemical  action  within  itself  or  with  any  other  component  of 
the  completed  cable. 

TESTS 

The  following  electrical  tests  shall  be  made  by  the  manufacturer 
at  his  works  and  without  expense  to  the  purchaser,  the  manu- 
facturer supplying  all  necessary  apparatus  and  the  purchaser 
to  have  the  privilege  of  being  represented  when  these  tests  are 
conducted.  The  manufacturer  shall  furnish  the  purchaser  with 
copies  of  data  sheets  showing  the  behavior  of  the  cable  during 
these  tests. 

(a)  Voltage  Test. — Each  length  of  cable  is  to  be  tested  with  alternating 
current,  having  a  frequency  preferably  the  same  as  that  of  the  system  of 


148     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

which  the  cable  is  to  be  a  part.  The  test  voltage  is  to  be  applied  between 
all  three  conductors  and  between  conductors  and  lead  sheath  at  a  tem- 
perature of  150°F.  If  the  cable  is  to  form  part  of  a  system  having  a  per- 
manently grounded  neutral,  the  neutral  point  of  the  test  generator  shall  be 
connected  to  the  cable  sheath  during  the  test.  If  the  cable  is  to  form  part 
of  a  system  with  an  ungrounded  neutral,  two  tests  shall  be  made,  the  first 
with  conductor  A,  the  second  with  conductor  B,  grounded  to  the  cable 
sheath.  The  apparatus  supplying  the  energy  for  the  voltage  test  must 
have  a  kilovolt-ampere  capacity  at  least  four  times  the  kilovolt-ampere 
capacity  absorbed  by  the  length  under  test,  and  in  any  event  must  not  be 
less  than  25  kva.  capacity.  The  time  of  application  of  the  test  and  test 
pressure  shall  be:  5  min.  at  a  voltage  having  a  peak  value  two  and  one- 
half  times  the  peak  value  of  the  normal  working  pressure  as  determined  by 
spark-gap  in  accordance  with  the  American  Institute  of  Electrical  Engineers 
Standardization  Rules. 

(6)  Insulation  Resistance  Test. — (1)  An  insulation-resistance  test  shall  be 
made  immediately  before  and  after  the  voltage  test.  (2)  The  measurement 
shall  be  made  with  a  direct-current  voltage  of  not  less  than  100  volts,  the 
reading  to  be  taken  after  1  min.  electrification,  and  shall  show  no  appreciable 
decrease  in  the  value  of  the  insulation  resistance  between  the  two  successive 
measurements.  Measurements  shall  be  made  between  each  conductor 
and  each  of  the  other  two  and  between  each  conductor  and  the  lead  sheath. 
Any  section  of  cable  which  shows  a  marked  variation  from  others  of  the 
same  type  manufactured  at  the  same  time  shall  be  held  for  further  examina- 
tion and  if  such  variations  cannot  be  satisfactorily  explained  the  section  shall 
be  rejected. 

(c)  Breakdown  Test. — Samples  from  10  to  25  ft.  long  and  selected  by  the 
purchaser  at  random  from  any  cable  lengths  shall  not  break  down  under 
five  times  the  working  pressure  applied  for  5  min.  between  all  three  con- 
ductors and  between  conductors  and  lead  sheath,  after  samples  with  ends 
sealed  have  remained  at  a  temperature  of  150°F.  for  100  hr.  in  straight  single 
lengths  with  axes  inclined  15°  to  the  horizontal. 

(d)  Bending  Test. — A  sample  from  any  length  of  cable  shall  be  bent  around 
a  cylinder  having  a  diameter  equal  to  15  times  the  outside  diameter  of  the 
cable  over  lead  sheath,  and  then  be  straightened  out.     It  shall  then  be  bent 
in  the  opposite  direction  around  the  cylinder  and  straightened  out.     This 
operation  shall  be  performed  twice  in  succession,  after  which  the  cable 
shall  be  capable  of  withstanding  a  voltage  test  two  and  a  half  times  working 
pressure  applied  for  a  period  of  5  min.  between  the  conductors  and  between 
the  conductors  and  the  lead  sheath,  and  shall  show  no  signs  of  mechanical 
injury  or  electrical  injury  when  dissected. 

Test  after  Installation. — The  cable  shall  be  capable  of  withstanding  twice 
normal  working  pressure  applied  between  all  three  conductors  and  between 
conductors  and  lead  sheath  for  a  period  of  10  min.,  after  being  drawn  into  the 
ducts  and  jointed.  An  insulation-resistance  test  shall  be  made  immediately 
before  and  after  the  breakdown  test,  using  the  method  specified  under  (6-2) 
above,  and  the  insulation  resistance  shall  not  be  materially  reduced  as  a 
result  of  this  test. 


CABLES  149 

Moisture  in  Cable  Insulation. — Some  companies,  in  their 
high-tension  paper-insulated  cable  specifications,  include  a  clause 
to  limit  the  percentage  of  moisture  in  the  insulating  compound. 
This  appears  to  be  a  step  in  the  right  direction  but  such  specifica- 
tions should  be  accompanied  by  an  exact  description  of  the 
method  to  be  employed  in  determining  the  percentage  of  water 
in  the  insulating  compound. 

Different  methods  of  tests  give  different  results,  some  of  which 
are  accurate  only  to  within  approximately  25  per  cent.  It  is 
evident  that  in  order  to  have  accurate  results  the  insulation 
must  be  removed  from  the  lead  and  copper  and  the  difficulty  is 
to  accomplish  this  without  exposing  the  insulation  to  the  air, 
thus  allowing  it  to  absorb  moisture,  so  that  tests  made  from  the 
same  cable  show  variations  in  accordance  with  the  percentage 
of  moisture  in  the  atmosphere  at  the  time  the  tests  are  made. 

In  the  production  of  high-grade  transformer  oils,  great  care 
is  used  to  eliminate  even  minute  percentages  of  moisture.  In 
ordinary  cases  Jfo  Per  cent,  is  considered  objectionable,  and  it 
is  believed  that  where  trouble  is  experienced  with  impregnated- 
paper  cables  it  is  due  to  the  lack  of  this  same  attention  to  the 
question  of  moisture  in  the  original  compound  or  in  the  paper 
itself. 

The  rosin  of  commerce  which  is  used  for  a  base  in  most  paper 
cables  is  the  residue  from  a  steam-distillation  process  for  turpen- 
tine and  contains  from  8  to  10  per  cent,  of  water.  The  rosins 
obtained  from  the  so-called  "dry  process"  contain  less  moisture 
than  this,  but  are  of  an  inferior  grade. 

In  usual  methods  of  making  rosin-oil  compound  the  mixture 
of  rosin  and  oil  is  heated  so  that  the  water  is  boiled  off.  This 
method,  if  carried  to  an  extreme,  may  result  in  the  reduction 
of  the  water  to  as  low  as  1  per  cent.,  but  in  common  practice  rarely 
reaches  this  minimum.  There  is  also  water  present  in  unstable 
molecular  combination  with  the  rosin  and  when  cable  is  operated 
above  normal  temperatures  this  molecular  condition  is  destroyed, 
and  actual  water  and  a  further  liberation  of  volatile  ingredients 
results.  This  fact  apparently  accounts  for  some  cable  troubles 
which  are  otherwise  unexplainable. 

However,  the  present-day  methods  of  paper-cable  manufacture 
have  reached  a  degree  of  perfection  where  very  little  trouble 
need  be  feared  from  overheating  due  to  the  presence  of  residual 
moisture  in  the  insulation,  if  the  cable  is  operated  within  the 


150     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

limits  of  voltage  for  which  it  has  been  designed.  Only  in  cases 
where  the  insulation  has  not  been  properly  treated  will  excessive 
dielectric  losses  be  noticed. 

Numerous  tests  have  been  made  to  determine  heating  due  to 
dielectric  losses,  but  in  no  case  have  these  losses  been  found  to 
be  abnormal  provided  the  cable  insulation  has  been  properly 
treated  and  applied. 

It  would,  therefore,  seem  that  there  is  no  good  reason  for 
believing  that  there  is  ever  enough  residual  moisture  in  the  cable 
insulation  to  cause  any  appreciable  increase  in  normal  dielectric 
hysteresis,  and  that  where  companies  are  experiencing  trouble 
of  this  nature  the  cause  is  not  due  to  residual  moisture  in  the 
compound,  but  to  moisture  entering  the  cable  after  installation, 
either  through  small  holes  in  the  lead  sheath,  or  when  joints  are 
made  under  unfavorable  conditions  in  damp  weather. 


CHAPTER  VI 
INSTALLATION  OF  CABLES 

Handling  Lead  Cables. — No  attempt  will  be  made  to  indicate 
all  the  details  of  cable  installation;  it  is  the  intention  rather  to 
outline  the  general  method  of  installing  underground  cables  and 
to  emphasize  the  importance  of  some  parts  of  the  work  in  con- 
nection therewith.  Cables  are  shipped  from  the  manufacturers 
on  wooden  reels  of  suitable  size  to  accommodate  one  or  more 
lengths  of  cable. 

When  coiling  a  cable  on  a  reel,  the  first  end,  usually  termed  the 
test  end,  is  put  through  a  slanting  smooth  hole  in  the  side  of  the 
reel  so  as  to  have  both  ends  of  the  cable  accessible  for  testing 
before  shipment.  After  testing,  both  ends  are  capped  or  sealed, 
thus  protecting  the  cable  insulation  from  moisture.  The  test 
end  of  the  cable  is  usually  left  protruding  through  the  side  of 
the  reel  from  12  to  18  in.  and  is  boxed  over.  It  is  customary  to 
lag  the  reel  from  flange  to  flange  with  heavy  wooden  slats  nailed 
to  the  flanges  and  further  secured  by  wires  encircling  the  slats 
to  protect  the  cable  thoroughly  from  injury  in  transit  or  while 
standing  on  the  street. 

Transporting  reels  of  cable  from  the  railroad  to  the  manhole 
should  be  entrusted  only  to  experienced  truckmen;  and  if  a  low 
wagon  is  not  available,  and  a  high  wagon  must  be  used,  the  reels 
of  cable  should  be  carefully  lowered  from  the  wagon  by  means  of 
a  windlass  and  skids  and  not  allowed  to  drop  to  the  ground.  To 
avoid  the  loosening  of  the  cable,  the  reels  should  be  rolled  in  the 
direction  of  the  point  of  the  arrow  painted  on  the  side  of  the  reel. 

The  reel  of  cable  is  then  placed  at  the  manhole,  over  the  duct 
into  which  the  cable  is  to  be  drawn,  in  such  a  way  that  the  cable 
will  unwind  from  the  top  of  the  reel.  It  should  next  be  mounted 
on  jacks  and  not  until  that  is  done  should  the  slats  be  removed, 
care  being  taken  that  no  nails  come  into  contact  with  the  cable 
or  are  left  in  the  flanges  to  do  damage. 

An  improved  form  of  jack  designed  to  handle  cable  reels  of 
varying  sizes  is  shown  in  Fig.  62.  It  is  provided  with  three 

151 


152     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

forged-steel  hooks,  as  well  as  a  swivel  top,  so  that  the  reel  can 
be  picked  up  on  the  hook  nearest  its  center  and  suspended  with 
a  very  small  amount  of  ratcheting,  at  the  same  time  being  just 
high  enough  to  clear  the  ground. 

A  pair  of  these  jacks  will  safely  support  cable  reels  of  any 
ordinary  size,  the  combined  safe  carrying  capacity  of  a  pair  being 


FIG.  62.— Reel  jack. 

over  6  tons  on  the  top  hook.  Reels  weighing  from  6  to  10  tons 
may  be  raised  on  the  swivel  top  or,  if  the  diameter  of  the  reel 
permits,  on  either  of  the  two  lower  hooks. 

The  jack  is  superior  to  the  screw  type  of  cable-reel  jack,  as  it 
raises  or  lowers  the  load  faster  and  by  the  use  of  the  hook  arrange- 
ment, which  is  not  applicable  to  an  ordinary  screw  jack,  one  pair 
of  jacks  can  handle  almost  any  size  reel. 

The  utmost  care  should  be  taken  not  to  bend  the  cable  sharply, 


INSTALLATION  OF  CABLES  153 

nor  to  break  through,  cut,  abrade,  kink  or  dent  the  lead  sheath; 
and,  above  all,  not  to  allow  the  slightest  trace  of  moisture  to 
enter  the  ends  of  the  cable  after  the  seals  have  been  broken.  A 
failure  to  observe  these  points  may  result  in  the  loss  of  the  cable. 
The  useful  life  of  an  underground  cable  is  determined  by  that  of 
the  insulation,  which  in  turn  usually  depends  upon  the  integrity 
of  the  lead  sheath. 

Choice  of  Ducts. — Before  drawing  cables  into  a  new  conduit 
system,  there  is  often  a  question  as  to  which  of  the  ducts  shall  be 
used  first.  Workmen,  when  about  to  install  cables,  may  have 
been  told  to  use  any  one  of  the  ducts,  and  naturally  they  draw 
the  cable  into  those  which  are  most  convenient,  without  any 
consideration  for  the  cables  which  are  to  be  installed  later. 
There  are  cases  where  a  manhole  has  been  completely  blocked 
by  the  first  few  cables  installed.  There  is  another  important 
reason  for  using  care  in  the  selection  of  the  ducts  to  be  used  for 
power  cables,  as  will  be  seen  from  the  following: 

It  is  not  possible  to  foretell  the  current-carrying  capacity  of 
a  cable  without  previous  knowledge  of  all  the  controlling  factors 
which  will  influence  temperature  rise  in  such  a  cable.  Some 
of  the  most  important  factors  are:  natural  temperature  of  the 
ducts  and  manholes;  amount  of  moisture  present;  condition  and 
action  of  soil  surrounding  the  conduit;  and  exact  location  of  the 
cable  in  the  conduit  with  respect  to  other  cables  which  have 
previously  been  installed.  All  of  these  greatly  influence  both  the 
radiation  and  dissipation  of  heat  generated  in  each  conductor  or 
cable  and  consequently  the  current-carrying  capacity  of  the 
conductor. 

Usually  the  ducts  which  dissipate  heat  most  rapidly,  and  there- 
fore run  coolest,  are  those  located  at  the  lower  corners  of  the 
conduit.  Those  nearest  to  the  outside  of  the  system  run  fairly 
cool,  but  the  middle  and  top  ducts,  which  not  only  take  up  heat 
from  the  lower  cables  but  must  dissipate  heat  through  adjoining 
ducts,  operate  at  a  fairly  high  temperature.  Attention  to  these 
points,  when  planning  a  new  system,  may  prove  very  profitable 
in  the  end. 

Regarding  the  selection  of  cables,  it  should  be  borne  in  mind 
that  other  conditions  being  equal,  those  insulated  with  rubber 
compound  dissipate  heat  more  readily  than  those  insulated  with 
paper  or  other  fibrous  material.  On  the  other  hand,  it  has  been 
found  that  a  cable  insulated  with  an  oil-saturated  paper  will 


154     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


operate  for  a  longer  time  at  a  high  temperature  without  deteriora- 
tion than  when  insulated  with  rubber  compound.  This,  however, 
does  not  hold  true  if  too  much  resinous  material  has  been  used  in 
making  up  the  paper  insulation. 

To  economize  in  space,  as  many  as  six  cables  are,  at  times, 
drawn  into  one  duct.  While  this  may  be  an  advantage,  it  is 
accompanied  by  the  danger  of  losing  all  six  cables  through  the 
failure  of  one. 

A  cable  should  never  be  drawn  over  one  already  in  position, 
as  the  wear  of  the  rubbing  lead  is  excessive;  and  one  cable, 


-O 


FIG.  63. — Rodding  sticks  and  snake  wire. 

usually  the  one  in  place,  is  almost  sure  to  be  damaged  by  the 
lead  being  worn  through. 

Rodding  Ducts. — After  having  decided  upon  the  duct  into 
which  the  cable  is  to  be  drawn,  preparations  are  made  to  wire  the 
duct  and  to  clean  it  thoroughly,  freeing  it  from  any  obstructions 
which  might  injure  the  cable  when  being  drawn  in.  To  accom- 
plish this,  a  snake  wire  or  rodding  stick,  of  which  there  are 
several  types,  Fig.  63,  is  worked  through  the  duct.  If  the  sec- 
tions between  manholes  are  short,  rods  are  not  required,  a 
snake  wire  alone  being  used.  The  latter  is  also  better  adapted 
to  wiring  ducts  with  curves,  but  cannot  be  used  in  very  long 
lengths  owing  to  the  friction  encountered.  By  means  of  a  gal- 


INSTALLATION  OF  CABLES  155 

vanized  wire  a  suitable  rod  to  which  is  attached  a  scraper, 
gage,  brush,  or  swab  is  next  drawn  through  the  duct  to  insure 
a  clear  passage  for  the  cable.  Gages  so  used  should  be  about 
%  in.  larger  than  the  cable  to  be  installed. 

It  is  customary  to  rod  long  sections  of  conduit,  using  wooden 
rods  about  1  in.  in  diameter  and  3  or  4  ft.  long,  provided  at  each 
end  with  coupling  devices  by  means  of  which  the  various  sec- 
tions may  be  jointed  together.  These  coupling  devices  consist 
of  either  screw  connections  or  a  sliding  coupling  which  may  be 
more  quickly  joined. 

The  method  of  rodding  is  as  follows : 

A  bundle  of  rods  is  placed  in  the  manhole;  a  workman  standing 
in  the  hole  pushes  one  rod  into  the  duct,  attaches  a  second  to  the 
first  and  pushes  it  ahead,  continuing  this  operation  until  the  first 
rod  appears  at  the  next  hole.  A  rope  is  then  fastened  to  the 
rod  at  the  distant  manhole  and  the  rods  with  the  rope  attached 
are  drawn  back  into  the  first  hole  and  disconnected  as  they  are 
drawn  from  the  duct  until  the  rope  appears.  If  a  large  quantity 
of  duct  is  to  be  rodded,  it  is,  of  course,  impracticable  to  draw  a 
rope  into  each  section,  yet  it  is  advisable  to  have  the  line  rodded 
somewhat  in  advance  of  the  cable  gang.  In  this  case  a  small 
piece  of  steel  wire  (No.  10  or  No.  12  B.W.G.)  is  drawn  into  the 
duct  by  the  rods  and  left  in  place  to  be  later  used  to  draw  in  the 
rope.  This  wire,  if  properly  handled,  and  drawn  out  and  reeled 
or  coiled  neatly,  may  be  used  several  times.  Obviously,  rods 
may  be  drawn  out  at  the  distant  manhole  and  there  disconnected 
from  the  wire  fed  in  at  the  first  hole.  This  method  is  usually 
adopted  when  a  long  straight  run  of  duct  is  to  be  wired,  the  rods 
being  shoved  into  the  next  duct  section  as  they  are  drawn  out  and 
disconnected  from  the  first  section.  If  the  ducts  are  in  a  straight 
line  across  the  manhole,  the  rods  may  often  be  passed  into  the 
next  section  without  disconnecting. 

Obstructions  in  Ducts. — A  completed  conduit  system  should 
always  be  tested  for  obstructions  previous  to  its  acceptance 
from  the  contractor  by  drawing  through  each  duct  a  test  mandrel 
about  24  in.  in  length  and  Y±  in.  less  in  diameter  than  the  bore 
of  the  duct. 

Ordinary  obstructions,  such  as  pieces  of  cement  or  dirt,  may 
be  removed  by  mounting  a  mandrel  consisting  of  a  piece  of  steel 
pipe  on  the  end  of  the  first  rod  and  drilling  away  the  projecting 
cement  Sometimes  obstructions  are  met  which  cannot  be  so 


156     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


removed.  These  must  be  located  by  a  measurement  of  the  rods 
pushed  into  the  ducts  until  the  trouble  is  reached,  the  street 
opened  at  that  point  and  the  ducts  repaired  or  replaced  by  new 
sections. 

Several  forms  of  mandrels  or  duct  cleaners  have  been  used,  but 
attention  is  called  to  Fig.  64  which  shows  a  flexible  cleaner  so 
designed  that,  when  drawn  through  the  conduit,  particles  of 
cement  are  broken  off  and  removed  from  the  duct.  It  is  usual, 
when  cleaning  ducts,  to  attach  to  the  cleaner  a  swab  or  brush 
of  some  sort  to  remove  properly  the  loose  particles  from  the  duct 
line. 


FIG.  64. — Flexible  duct  cleaner. 

Drawing  in  Cables. — Before  drawing  the  cable  into  the  duct 
the  ends  should  be  examined  to  see  that  they  are  perfect.  A  wire- 
pulling grip  of  some  form  is  then  drawn  through  the  cable  end. 
To  the  end  of  this  grip  is  next  fastened  a  flexible  steel  or  manila 
pulling-rope,  which  in  the  meantime  has  been  drawn  through  the 
duct  ready  for  pulling.  Proper  cable  protectors  are  placed  in 
the  mouth  of  the  duct.  These  protectors  are  usually  made  of 
leather  and  placed  in  the  end  of  the  duct  to  prevent  damage  to 
the  sheath.  The  cable  from  the  top  of  the  reel  should  enter  the 
mouth  of  the  duct  by  a  curve  of  large  radius,  Fig.  65,  without 
touching  at  any  intermediate  point.  The  pulling  can  be  done 
by  capstan,  winch,  motor  truck,  horses,  or,  in  the  case  of  a 
small  cable,  by  hand.  When  guiding  the  cable  into  the  duct,  a 
small  amount  of  common  grease  should  be  spread  on  the  cable 
so  as  to  allow  it  to  slide  more  easily  and  lessen  the  strain  on  the 
cable.  Enough  extra  cable  should  be  drawn  into  the  manhole 
to  provide  for  racking  around  the  manhole  and  the  making  of 
joints.  During  the  installation,  no  cable  should  be  bent  sharper 


INSTALLATION  OF  CABLES 


157 


than  to  a  radius  equal  to  ten  diameters  of  the  cable.  If  it  is  not 
intended  to  joint  the  cables  as  soon  as  they  are  drawn  in,  the  caps 
or  seals  should  be  examined  to  see  that  they  are  safe  before  leav- 
ing the  work.  The  cable  should  be  protected  at  the  edge  of  the 
duct,  and  should  not  be  left  hanging  loosely  or  lying  on  the  bottom 
of  the  manhole,  but  should  be  placed  on  the  racks  provided  for  it. 
Paper-insulated  cables  should  not  be  installed  at  temperatures 
below  40°F.  without  first  warming  them  up  by  charcoal  fires,  or 
other  means,  so  as  to  make  them  more  flexible  and  avoid  any 
possibility  of  cracking  the  insulation.  Also  when  cables  are  being 
racked  around  the  manhole  wall  they  should  be  thoroughly 
warmed  if  the  temperature  is  low.  Before  jointing,  the  ends 
should  be  cut  back  far  enough  to  positively  insure  against  the 
presence  of  moisture.  No  matter  how  excellent  a  cable  the 


FIG.  65. — Setting  up  cable  reel. 

manufacturer  may  produce,  if  it  is  not  carefully  installed  and 
properly  cared  for  thereafter,  it  will  inevitably  fail,  and  it  is, 
therefore,  necessary  that  the  work  be  done  by  experienced  and 
reliable  workmen.  It  will  generally  be  found  more  satisfactory 
for  a  small  company  to  have  its  cables  installed  by  the  manu- 
facturer. A  large  company,  however,  frequently  finds  it  cheaper 
to  install  its  own  cables.  All  large-sized  cables  should  be  ordered 
in  exact  lengths,  making  the  proper  allowance  for  training  in 
manholes  and  necessary  waste. 

Cable-pulling  Grips. — Many  devices  for  fastening  the  cable 
and  draw  rope  together  have  been  used  and  abandoned  as  un- 
reliable. Where  the  ducts  are  dry,  a  good  serviceable  grip  is 
obtained  by  punching  two  holes  through  the  center  of  the  cable 
from  side  to  side,  the  holes  being  spaced  about  3  in.  away  from 
each  side  of  the  cable  end.  A  No.  10  or  No.  12  B.W.G.  steel 


158     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

wire  is  then  passed  several  times  through  the  eye  of  the  rope 
and  the  holes  in  the  cable,  and  the  ends  of  the  wire  are  twisted 
firmly  together.  This  method  is  not  recommended  where  there 
is  any  danger  of  water  in  the  ducts,  as  the  water  is  certain  to 
enter  the  cable  through  the  holes;  and  in  case  of  paper  cable, 
to  penetrate  so  far  that  the  ends  often  cannot  be  cut  back  far 
enough  to  clear  the  trouble  thus  introduced.  A  better  form  of 
grip,  and  the  one  which  is  used  almost  universally  to-day  is  shown 
in  Fig.  66 A. 


FIG.  66. — Wire-cable  grips. 

A  block  of  wood  about  3  in.  wide  is  placed  against  the  end  of 
the  cable,  and  steel  wire  of  No.  10  or  No.  12  B.W.G.  cut  in 
6-ft.  lengths  is  then  bent  in  the  middle  of  the  wood  block  and 
wrapped  around  the  cable  sheath  in  opposite  directions,  the 
number  of  wires  required  depending  on  the  severity  of  the  pull. 
When  the  pull  of  the  rope  comes  on  these  wires,  they  bind  harder 
on  each  other,  on  the  lead,  the  insulation,  and  the  conductors, 
as  the  pull  grows  harder,  and  the  strain  is  equally  distributed. 


INSTALLATION  OF  CABLES 


159 


With  this  type  of  grip,  the  seal  on  the  lead  of  the  cable  is  not 
broken  and  no  water  can,  therefore,  get  into  the  insulation.  A 
form  of  basket-wire  grip  which  has  been  used  to  good  advantage 
is  illustrated  in  Fig.  66,  B,  D,  E. 

Where  a  section  of  cable  is  to  be  installed  in  a  duct  of  a  bore 
only  slightly  larger  than  the  diameter  of  the  cable,  the  ordinary 
woven-wire  cable  grip  often  fails,  the  reason  for  its  failure  being 
that  the  diameter  of  the  cable  is  increased  by  the  wire  of  the 
grip  leaving  insufficient  clearance.  The  excessive  strain,  more- 
over, has  a  tendency  to  strip  the  lead  sheath  from  the  cable. 


FIG.  67. — Construction  of  a  cable  grip  suitable  for  pulling  cables  up  to 
2^  inches  outside  diameter. 

Considerable  thought  has  been  given  to  the  various  methods 
utilized  in  fastening  the  pulling-rope  to  the  cable  ends  when  large- 
sized  cable  is  to  be  pulled  into  a  duct  line.  A  very  satisfactory 
method  is  to  use  what  is  known  as  a  cable  eye.  This  cable  eye 
is  made  of  round  steel  about  %  in.  in  diameter,  and  an  eyelet, 
approximately  1^  in.  in  size  turned  on  one  end.  The  proper 
procedure  to  be  followed  in  fastening  this  eyelet  to  the 
cable  is  to  strip  back  the  lead  sheath  6  or  8  in.,  remove  the 
insulation  from  the  conductors,  then  place  the  eyelet  between  the 
conductors  and  wind  them  securely  around  it  and  solder  them 
fast.  Next  the  portion  of  the  lead  sheath,  which  was  stripped 
back,  is  moulded  around  the  conductors  and  eyelet,  the  whole 


160     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

soldered  and  sealed  so  that  it  is  waterproof.  In  using  this  eyelet 
all  the  strain  is  placed  on  the  conductors  and  there  is  no  danger 
of  moisture  entering  the  cable  during  the  process  of  installation 
due  to  damaged  ends  or  improper  seals. 

What  may  be  termed  a  "basket  grip"  is  described  in  the 
Electrical  World,  March  25,  1916.  This  grip  may  be  cast  of  iron 
or  phosphor  bronze.  The  grip  illustrated  in  Fig.  67  is  suitable 
for  pulling  cables  having  an  outside  diameter  up  to  2%  in. 
About  4  in.  of  the  lead  and  insulation  is  cut  away  from  the  end 
of  the  cable  and  the  bare  conductors  are  tinned  and  pushed 
up  through  the  basket.  The  conductors  are  then  spread  in  the 
upper  part  of  the  basket,  which  is  tapered  to  accommodate  this 
process  and  molten  solder  is  poured  over  the  spread  conductors. 
After  the  solder  has  cooled,  the  hooks  attached  to  the  pulling- 
rope  are  passed  through  the  loop  of  the  basket,  and  the  cable 
can  then  be  drawn  through  the  ducts.  However,  if  the  duct  is 
wet  or  muddy,  it  is  best  to  prevent  water  getting  into  the  cable 
end  by  winding  a  good  quality  of  rubber-filled  tape  around  the 
lower  end  of  the  basket  and  the  adjacent  lead  sheath  of  the 
cable. 

If  the  cable  to  be  installed  is  single-conductor  instead  of  multi- 
conductor,  the  basket  grip  is  equally  adaptable.  The  method 
of  procedure  is  similar  to  the  above,  and  the  cable  can  be  pre- 
vented from  slipping  out  of  the  basket  by  spreading  the  individual 
strands  of  the  conductor. 

Draw  Rope. — For  general  purposes  a  manila  rope  of  best 
quality  and  from  %  to  1J^  in.  in  diameter  will  be  found  most 
satisfactory  for  pulling  in  cables.  A  steel  hoisting  rope  is  some- 
times used,  but  it  deteriorates  rapidly  from  rust  and  hard  usage 
on  the  street  unless  protected  by  some  form  of  covering.  What- 
ever style  of  rope  is  used,  the  ends  should  be  provided  with  an 
"eye"  around  a  steel  thimble  fastened  to  a  short  length  of  chain 
provided  with  a  swivel  at  the  end.  In  very  hard  pulls  any  rope 
tends  to  untwist,  and  unless  a  swivel  is  inserted  between  the  rope 
and  cable,  this  twist  will  be  imparted  to  the  cable  itself  and  may 
injure  the  lead  or  the  conductors.  It  is  advisable  to  terminate 
the  swivel  with  a  pair  of  sister-hooks,  Fig.  68.  These  are  readily 
inserted  in  the  loop  of  the  wire  grip  on  the  cable  and  prevented 
from  opening  by  several  wraps  of  wire. 

What  is  known  as  a  "durable  steel-stranded"  rope  is  used  by 
a  number  of  companies  for  pulling  in  cable.  The  rope  is  made  up 


INSTALLATION  OF  CABLES 


161 


with  a  flexible  core  and  the  strands  are  covered  with  specially 
prepared  braided  hemp,  which  binds  the  strands  together  forming 
a  cushion  between  strands  and  protecting  the  rope  from  wear. 
The  rope  is  rustproof  and  will  outwear  a  number  of  coils  of 
ordinary  manila  rope.  The  ^-in.  size  replaces  the  ordinary 
IJ^-in.  manila  rope.  It  is  especially  desirable  when  power- 
driven  winches  are  used. 

Drawing  Apparatus. — If  the  cable  is  light  and  short,  it  may  be 
pulled  in  by  hand,  but  usually  some  apparatus  will  be  found 
necessary  to  secure  sufficient  power. 

Horses  are  sometimes  used  to 
haul  in  the  cable  by  hitching  them 
directly  to  the  cable  rope  which 
passes  from  the  manhole  over 
snatch  blocks  or  sheaves.  This 
method  is  undesirable  as  it  is  im- 
possible to  stop  horses  instantly  in 
case  of  an  accident  to  the  reel  or 
to  the  cable  at  the  mouth  of  the 
duct,  or  in  case  of  meeting  other 
unforeseen  obstructions;  and  serious 
damage  to  the  cable  is  liable  to 
ensue. 

In  some  cities  where  great  quan- 
tities of  cable  are  installed  yearly, 
winches  as  shown  in  Fig.  69  run  by 
electricity  or  gasoline  engines 
mounted  on  a  wagon,  are  used  for 
pulling  in  the  cables,  but  this  de- 
vice is  too  expensive  in  the  first 
cost  and  maintenance  for  profitable  use  unless  large  quantities 
of  cable  are  handled  regularly. 

For  drawing  in  underground  cables,  in  many  locations  a  small 
ship's  capstan  mounted  on  a  stout  framework  fastened  to  the 
pavement  has  been  used.  The  frame  on  which  the  capstan  is 
fastened  is  provided  with  wheels  easily  removable  to  facilitate 
moving  the  apparatus  from  place  to  place.  The  draw  rope  is 
led  over  pulleys  from  the  duct  in  the  manhole  to  the  capstan  on 
the  street  and  is  wrapped  several  times  around  the  drum  to  give 
the  required  purchase.  The  power  is  furnished  by  men  in  the 
regular  way. 
11 


FIG.  68.— Sister  hooks. 


162     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


In  some  locations  manholes  are  so  near  car  tracks  or  other 
obstacles  that  there  is  not  sufficient  space  for  either  form  of 
capstan  with  the  projecting  handle  bars.  In  such  cases  a  winch, 


FIG.  69. — Electric  motor-driven  winch. 

Fig.  70,  mounted  on  a  strong  framework  is  most  convenient. 
The  framework  is  placed  directly  over  the  manhole  opening  and 
the  rope  is  led  from  the  duct  through  a  snatch  block  directly  to 
the  drum  of  the  winch,  the  power  being  applied  by  two  cranks 


FIG.  70. — Hand  winch. 

(revolving  handles)  one  on  each  side  of  the  drum  and  directly 
opposite  each  other,  so  placed  that  when  one  crank  is  down  the 
other  is  up.  The  snatch  block  in  the  manhole  may  be  fastened 


INSTALLATION  OF  CABLES 


163 


in  place  by  attaching  it  to  eye-bolts  built  into  the  walls  or  by 
suitable  blocking. 

When  constructing  manholes,  it  is  advisable  to  provide  facili- 
ties for  drawing  cables  through  ducts  so  that  special  guide  sup- 
ports do  not  have  to  be  used.  The  accompanying  illustration, 
Fig.  71,  shows  how  manholes  may  be  equipped  for  this  purpose. 
In  the  wall  opposite  and  about  12  in.  below  each  duct  entrance 
is  an  eye-bolt  which  extends  through  the  wall  and  is  bent  over 
on  the  end  to  bear  on  an  iron  plate  which  reduces  the  unit  pressure 


FIG.  71. — Diagram   showing   equipment   of   manhole   to   facilitate   cable 

installation. 

on  the  manhole  wall.  This  eye-bolt  may  be  employed  to  support 
a  guide  block  during  the  usual  installation  of  a  cable,  or  it  may 
be  connected  to  a  block  and  tackle  when  it  is  necessary  to  draw 
a  cable  into  place  for  splicing  in  cases  where  sufficient  length  has 
not  been  left  for  this  operation. 

A  flexible  arrangement  of  the  pulleys  may  be  secured  by  means 
of  two  steel  channels  or  guide  sheaves  of  such  length  as  to  reach 
from  the  bottom  of  the  manhole  to  a  point  about  3  ft.  above 
the  surface  of  the  ground.  The  channels  are  provided  with 
holes  every  few  inches  along  the  entire  length,  through  which 
heavy  steel  [pins  secured  by  cotter  pins  may  be  placed,  thus 


164     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

providing  movable  shafts  for  the  pulleys,  as  shown  in  Fig.  72. 
The  lower  pulley  is  placed  opposite  the  duct  and  the  rope  leav- 
ing the  duct  passes  under  this  pulley  up  to  and  over  the  upper 
pulley  just  above  the  street  surface.  The  bottoms  of  the  chan- 


\ 


Hot.es 


FIG.  72. — Guide  sheave  for  cable  pulling. 

nels  rest  against  the  wall  of  the  manhole  and  the  tops  against 
the  manhole  cover  frame. 

Power  Trucks. — In  the  1916  report  of  the  National  Electric 
Light  Association  Committee  on  Underground  Construction, 
under  the  heading,  "  Use  of  Power  Trucks  for  Underground  Work  " 
the  following  data  is  given.  Of  the  12  large  operating  companies 


INSTALLATION  OF  CABLES  165 

reporting,  all  use  power  trucks  for  their  cable  work.  Nearly 
all  companies  use  electric  trucks,  but  some  use  both  electric  and 
gasoline  engine-driven  trucks. 

The  electric  truck  most  suitable  for  underground  work  should 
have  a  speed  of  10  to  12  miles  an  hour,  and  designed  to  run  at 
least  35  miles  on  one  charge. 

In  addition  to  the  use  for  pulling  in  cable,  the  trucks  are  used 
for  hauling  reels  of  cable  to  the  jobs,  delivering  material,  and  for 
emergency  work.  Specially  designed  bodies  with  compartments 
for  tools  are  very  desirable,  Fig.  73.  Compartments  may  be 
built  along  both  sides  of  the  truck  to  hold  tools,  fire  extinguishers, 
sand  buckets,  etc.  A  compartment  for  the  records  of  the  dis- 


FIG.  73.— Cable  truck. 

tribution  system  may  also  be  provided  and  so  arranged  that  the 
cover  of  the  pocket  forms  a  desk  on  which  the  records  rest  while 
being  used  by  the  emergency  man. 

There  are  two  methods  of  pulling  in  cable : 

1.  By  means  of  pulleys  set  on  I-beam  uprights. 

2.  By  means  of  a  pulley  or  snatch  block  anchored  in  some 
manner  in  the  manhole. 

In  Fig.  74  is  illustrated  various  ways  of  arranging  the  trucks 
and  cable-pulling  apparatus  which  represents  the  practice  of 
several  of  the  large  electric  companies. 

When  manholes  are  near  car  tracks,  it  is  sometimes  impossible 
to  use  the  I-beam  upright  method  of  pulling  cable  without  inter- 
fering with  street-car  traffic.  For  this  reason  it  is  a  good  plan 


166     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


to  have  the  truck  equipped  with  facilities  for  pulling  cable  with 
a  rope  leading  from  the  rear  or  from  the  front.  A  New  York 
company  has  its  trucks  provided  with  facilities  for  pulling  from 
either  side  as  well. 


MILWAUKEE 


NEWARK 


BOSTON 


DETROIT 


Side  or  Ends 


NEW  YORK 


SAN  FRANCISCO 


CHICAGO  BROOKLYN 

ALL  TRUCKS   ARE  ELECTRIC    UNLESS  OTHEWISE    SPECIFIED 
MOTOR   WINCH   SHOWN   SOUD 


FIG.  74. — Methods  of  pulling  cable.1 

Some  difficulty  has  been  encountered  in  maintaining  the  I- 
beam  uprights  in  position  when  pulling  heavy  cable  on  account 
of  the  enormous  strain.  In  order  to  obviate  this  difficulty,  a 
Chicago  company  has  devised  an  anchor  with  wing  bolts  that  may 
be  adjusted  to  any  manhole.  This  anchor  holds  the  uprights  in 

1  N.  E.  L.  A.  Report,  1916. 


INSTALLATION  OF  CABLES  167 

position  by  a  strain  on  the  roof  of  the  hole,  as  illustrated  in  the 
figure. 

When  the  rope  is  passed  through  the  hole  in  the  floor  of  the 
truck,  the  strain  on  the  truck  as  well  as  on  the  winch  is  downward 
and  very  little  difficulty  is  experienced  in  holding  the  winch  to 
its  fastenings.  When  this  method  is  used,  the  truck  is  placed 
over  the  manhole,  a  position  which  takes  up  less  working  space 
in  the  streets  and  eliminates  the  hazard  of  injuries  to  pedestrians 
on  account  of  an  unprotected  open  manhole.  It  may  be  difficult 
to  design  the  truck  so  that  the  rope  leading  directly  downward 
through  the  trap  door  will  not  interfere  with  the  battery  or  run- 
ning gear.  Having  a  rolling  spool  for  the  rope  on  the  side  of  the 
truck  and  an  eye-bolt  for  a  snatch  block  in  the  center  of  the 
floor,  a  method  which  a  New  York  company  uses,  accom- 
plishes the  same  results  as  the  trap-door  method  without  intro- 
ducing its  objectionable  features.  To  prevent  accident,  cable- 
pulling  winches  which  are  motor-driven  should  have  all  of  the 
gears  or  movable  parts  covered  with  guards. 

It  is  recommended  that  trucks  for  underground  work  be 
wired  with  socket  for  an  extension  cord  to  both  the  front  and  the 
rear  of  the  truck.  This  will  greatly  facilitate  locating  trouble 
at  night.  For  splicing  cable  at  night,  however,  a  portable 
storage  battery  outfit  is  more  suitable  and  efficient.  The  use  of 
an  outfit  of  this  kind  eliminates  the  hazard  encountered  by  the 
use  of  candles  or  lanterns  in  gassy  manholes,  besides  providing 
the  light  necessary  for  good  jointing  work. 

Most  central  stations  have  provided  charging  stations  for 
electric  vehicles  throughout  their  territory.  Where  the  territory 
is  not  too  great,  one  central  charging  station  is  adequate  for  a 
truck  that  will  make  35  miles  on  one  charge.  A  boosting  charge 
during  the  noon  hour,  however,  is  recommended  where  the 
facilities  are  at  hand. 

Slack. — Enough  slack  must  be  left  in  each  manhole  to  enable 
the  cables  to  pass  around  the  sides,  to  make  and  place  the  joints 
on  the  wall  supports  and  to  keep  the  center  of  the  hole  free  from 
cables.  When  extra  slack  is  needed,  employ  a  short  rope  with 
one  end  frayed  for  5  or  6  ft.  and  wrap  the  soft  end  spirally 
around  the  cable  near  the  duct  so  as  to  obtain  a  tight  grip  with- 
out denting  or  kinking  the  cable.  Pass  the  rope  around  the 
capstan  or  winch  and  draw  the  cable  out  until  the  fastening 
reaches  the  drum  or  block,  slip  the  hitch  back  to  the  duct  and 


168     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

repeat  the  operation  until  sufficient  cable  has  been  secured. 
Always  determine  the  location  of  the  splice  in  the  manhole  and 
provide  the  foreman  of  the  drawing-in  gang  with  a  diagram  and 
list  showing  exactly  how  much  cable  should  project  from  the 
duct  into  the  manhole  at  each  end  of  each  section. 

After  a  cable  has  been  drawn  in,  an  experienced  workman 
should  examine  the  ends  to  see  if  the  solder  seal  is  intact  or,  if 
broken,  whether  any  moisture  is  present.  If  moisture  is  dis- 
cernible, boil  it  out  thoroughly  or  (if  enough  stock  is  available) 
cut  back  the  cable  until  all  dampness  is  removed;  and  in  all  cases 
leave  the  end  carefully  soldered  up. 

The  cable  should  be  protected  at  the  edge  of  the  duct,  and  it 
should  not  be  left  hanging  loosely  or  lying  on  the  bottom  of 
the  manhole,  but  should  be  placed  on  the  racks  provided  for  it. 
If  the  cables  have  paper  insulation  and  the  temperature  is  below 
40°F.,  they  should  be  warmed  by  torch  or  other  means,  so  as  to 
make  them  more  flexible  and  avoid  any  possibility  of  cracking  the 
insulation  when  the  cables  are  being  racked  around  the  manhole 
walls. 

Jointing  of  Cables. — It  is  generally  admitted  that  the  greater 
part  of  cable  trouble  is  due  to  poorly  made  joints  or  to  the 
presence  of  moisture  or  cracks  in  the  insulation  near  the  joints. 
With  good  material  and  careful  and  competent  workmen,  the 
insulation  of  the  joint  can  be  made  as  reliable  and  as  durable 
as  that  of  any  part  of  the  cable.  The  construction  of  a  joint 
is,  therefore,  of  prime  importance,  and  unless  the  engineer  has 
at  his  command  experienced  and  thoroughly  reliable  cable  work- 
men, he  would  do  well  to  contract  with  the  manufacturers,  who 
have  every  facility  for  doing  this  class  of  work,  for  the  complete 
installation  of  the  cable. 

In  the  making  of  a  perfect  joint,  the  following  points  are 
especially  worthy  of  comment  and  caution : 

(a)  The  work  should  be  done  by  reliable  and  experienced 
cablemen. 

(6)  High-grade  insulating  materials  should  be  carefully  chosen 
to  suit  the  special  conditions. 

(c)  Every  trace  of  moisture  should  be  excluded  from  the 
joint  and  adjacent  parts  of  the  cable. 

(d)  The  layers  of  insulating  tape  should  be  made  to  overlap 
each  other  and  should  be  drawn  tight  to  exclude  air. 


INSTALLATION  OF  CABLES 


169 


(e)  The  sleeve  should  be  well-filled  with  suitable  compound 
which  should  be  sufficiently  hot  before  pouring. 

(/)  The  joint  should  be  in  proportion  to  the  size  of  the  conduc- 
tor, and  the  insulation  on  the  joint  should  be  at  least  20  per  cent. 


LEAD  SLEEVE 

COMPOUND 

LEAD      '/^LATION        | 
SHEATH/                                i/ 

JC 

INT  INSULATION 
COPPER  SLEEVE 

OPENING  FOR  COMPOUND 
/  (|                              WIPED  JOINT 

Straight-way  single-conductor  cable  joint. 


Single-conductor  Y-shape  branch  joint. 


Single-conductor  right-angle  branch  joint. 


Two-parallel-conductor  branch  joint. 

FIG.  75. — Various  types  of  cable-joint  construction. 

thicker  than  on  the  cable  itself.     Fig.  75  illustrates  various  types 
of  joint  construction. 

While  not  a  part  of  joint  making,  it  is  perhaps  well  to  say  a 
few  words  regarding  the  training  of  cables  in  manholes.  Great 
care  should  be  exercised  in  bending  cables  into  position.  Sharp 


170     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


Two-right-angle  conductor  branch  joint. 


Straight-way  three-conductor  cable  joint. 


Three-conductor  right-angle  branch  joint. 


Insulated  single-conductor  cable  connection  to  a  bare  cable. 

FIG.  75.— (Continued.) 


INSTALLATION  OF  CABLES  171 

bends  in  high-voltage  cables  should  be  avoided,  and  the  cable 
should  never  be  bent  against  the  edge  of  the  duct  but  should  be 
shaped  around  a  form  to  avoid  abrading  the  lead.  It  should  be 
the  duty  of  the  jointer  to  see  that  protectors  of  some  sort  are  left 
under  the  cable  at  the  edge  of  the  duct  to  act  as  a  cushion .  Care- 
lessness in  observing  the  above  precautions  is  frequently  the 
cause  of  considerable  trouble. 

GENERAL  DIRECTIONS  FOR  MAKING  JOINTS  ON  LEAD- 
COVERED  CABLES 

The  cables  are  usually  left  by  the  pulling-in  gang  without  very 
much  reference  to  final  arrangement,  and  it  should  be  the  jointer's 
first  duty  to  inspect  the  cable  thoroughly  from  the  edge  of  the 
duct  to  the  sealed  end  in  order  to  discover  any  mechanical  injury 
or  intrusion  of  moisture.  Where  there  are  several  cables  to  be 
jointed  in  one  hole,  care  must  be  exercised  that  the  corresponding 
incoming  and  outgoing  sections  are  spliced  together.  Absurd 
as  it  may  seem,  such  mistakes  are  sometimes  made.  After  plac- 
ing protectors  in  the  mouth  of  the  ducts,  the  cables  should  be 
neatly  bent  and  stored  around  the  sides  of  the  manhole  and  the 
ends  brought  into  position  for  jointing  at  the  designated  point 
which  should  always  be  such  that  the  joint,  when  finished,  will 
be  between  two  supports  or  hangers  so  that  there  will  be  no 
strain  on  the  joint  itself  when  completed  and  stowed  away. 

When  the  ends  of  the  cables  have  been  allowed  to  lie  for  any 
length  of  time  in  manholes  where  there  is  water,  a  very  slight 
imperfection  in  the  soldered  end  will  admit  more  or  less  moisture 
to  the  insulation.  A  careful  examination  should  always  be  made, 
and  if  any  moisture  is  evident,  the  cable  should  be  cut  back  a 
little  at  a  time  until  all  evidence  of  moisture  disappears,  care 
being  taken  not  to  cut  back  so  far  as  to  render  it  too  short  to 
make  the  joint.  When  no  more  cable  can  be  cut  off  and  moisture 
is  still  present,  as  shown  by  bubbles  when  the  cable  is  dipped  into 
hot  insulating  compound,  apply  heat  to  the  lead  cover  of  the  cable, 
beginning  at  the  point  nearest  the  duct  and  very  slowly  approach- 
ing the  end  of  the  cable,  the  object  being  to  drive  all  moisture  to 
the  open  end.  Wherever  it  is  allowable,  a  furnace  or  gasoline 
torch  may  be  used  for  this  purpose;  and  if  the  cable  is  covered 
with  saturated  fiber,  a  metal  screen  should  be  interposed  between 
the  flame  and  the  cable  to  prevent  ignition  of  the  fiber.  If  the 


172     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

use  of  a  furnace  or  torch  is  forbidden,  or  it  is  unsafe  on  account 
of  the  presence  of  gas,  the  heating  should  be  effected  by  pouring 
very  hot  insulating  compound  over  the  cable,  catching  it  in  a 
vessel  held  underneath.  Where  there  is  still  doubt  as  to  freedom 
from  moisture,  it  is  best  to  make  a  careful  insulation  test  before 
the  joint  is  made.  This  test  may  indicate  the  necessity  of  re- 
placing the  cable  section.  Never  cut  off  the  second  section  until 
sure  that  there  is  no  moisture  in  the  first.  There  will  thus  be  an 
opportunity  to  change  the  location  of  the  splice  in  case  tjje  other 
end  must  be  cut  back  for  moisture. 

SCORING  THE  LEAD 

When  the  cables  are  placed  in  position  and  ready  for  joint, 
the  ends  should  be  marked  at  the  point  to  which  the  lead  is  to 
be  removed,  and  scored  or  cut  entirely  around.  This  cutting  is 
easily  and  accurately  accomplished  by  means  of  a  tool  which 
works  on  the  principle  of  an  ordinary  pipe  cutter. 

REMOVING  THE  LEAD 

The  lead  sheath  is  then  cut  lengthwise  of  the  cable  from  the 
circular  score  to  the  end  by  the  chipping  knife,  and  the  piece  of 
lead  is  removed  with  a  pair  of  pliers.  In  making  the  longitudinal 
cut  which  goes  entirely  through  the  lead,  great  care  must  be 
exercised  not  to  injure  the  insulation.  The  knife  should  be  held 
at  such  an  angle  that  it  will  go  through  the  lead  tangent  to  the 
insulation  (i.e.,  so  that  the  knife  will  pass  between  the  insulation 
and  the  lead  and  not  cut  the  insulation) ,  or  a  special  tool  may  be 
used. 

After  the  lead  has  been  removed,  the  parts  where  the  lead  was 
scored  should  be  carefully  examined  and  all  sharp  edges  or  pro- 
jections, which  might  tend  to  penetrate  the  insulation  of  the  cable, 
should  be  removed  by  a  knife,  or  the  lead  should  be  slightly 
belled  out  by  some  blunt  instrument  such  as  the  end  of  a  pair  of 
pliers. 

LEAD  SLEEVE 

When  the  lead  covers  of  the  two  cable  sections  have  been 
thus  treated,  a  lead  sleeve,  which  will  later  be  used  in  jointing, 
is  slipped  over  the  more  convenient  end  and  pushed  back  out  of 
the  way.  The  lead  of  this  sleeve  should  be  at  least  as  thick  as 


INSTALLATION  OF  CABLES 


173 


the  lead  of  the  cable  itself,  and  in  view  of  its  exposed  position, 
may  (in  the  case  of  thin  lead  on  the  cable)  be  made  somewhat 
heavier  to  give  greater  mechanical  strength. 

Before  slipping  it  on  the  cable,  each  end  of  the  sleeve  is 
thoroughly  scraped  with  a  shave  hook  or  knife  for  a  length  of 
about  2  in.,  and  the  cleaned  portion  thoroughly  smeared  with 
some  suitable  flux  (usually  a  tallow  candle),  which,  by  prevent- 
ing the  formation  of  the  usual  film  of  lead  salts,  insures  a  close 
union  of  the  lead  and  the  wiping  metal  which  is  used  to  make  the 
joint  between  sleeve  and  cable  sheath.  The  internal  diameter 
of  the  sleeve  should  exceed  the  diameter  over  the  lead  of  the  cable 
by  y%  in.  in  the  case  of  single-conductor  cables,  and  by  1  to  1J^ 
in.  in  the  case  of  multi-conductor  cables,  or  cables  for  high  voltage 
where  high  insulation  of  the  splice  and  maximum  separation 
between  the  conductors  and  lead  are  necessary.  The  following 
Table  XXIV  is  somewhat  more  liberal  in  allowances  for  clearance 
between  inside  of  sleeve  and  outside  of  cable,  but  it  is  fairly 
representative  of  average  practice  in  this  respect,  as  well  as  in 
the  sleeve  lengths. 


TABLE  XXIV. — APPROXIMATE  DATA  AS  TO  LEAD  SLEEVES,  WEIGHTS  OP 
SOLDER  AND  SPLICING  COMPOUND  FOR  STRAIGHT  JOINTS   (Two-WAY)1 


Outside  diam. 
of  cable,  mils 

Inside  diam 
sleeve,  in. 

Length  of 
sleeve,  in. 

Ozite  per 
joint,  gal. 

Wiping  sol- 
der   per 
joint,    Ib. 

• 

Single  conductor  E.  L.  & 

Up  to  550 

1 

8 

0.05 

0.9 

P.,  up  to  6,600  volts.  . 

551—    950 

1M 

10 

0.10 

1.7 

951—1,350 

2 

12 

0.20 

2.8 

1,351—1,750 

2H 

12 

0.30 

4.2 

1,751—2,150 

3 

14 

0.50 

5.5 

2,151—2,550 

SH 

14 

0.60 

6.8 

Single  conductor  E.  L.  & 

Up  to  550 

i 

10 

0.05 

0.9 

P.,  above  6,600  volts.  . 

551—   950 

1M 

12 

0.10 

1.7 

951—1,350 

2 

14 

0.20 

2.8 

1,351—1,750 

2H 

16 

0.40 

4.2 

' 

1,751  —  2,150 

3 

18 

0.60 

5.5 

2,151—2,550 

m 

18 

0.80 

6.8 

Multi-conductor  E.  L.  & 

Up  to  800 

IH 

14 

0.20 

1.5 

P  ,  all  voltages 

801  —  1,200 

2 

16 

0.25 

2.5 

1,201—1,600 

2H 

16 

0.35 

3.7 

1,601—2,000 

3 

18 

0.60 

5.0 

2,001—2,400 

m 

18 

0.80 

6.3 

2,401—2,800 

4 

18 

1.00 

7.6 

2,801—3,200 

4H 

20 

1.40 

8.3 

Standard  Underground  Cable  Co. 


174     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

COPPER  CONNECTORS 

One  of  the  important  features  to  be  considered  in  the  making 
of  joints,  as  already  mentioned,  is  in  the  choice  of  proper  copper 
jointing  sleeves.  They  should  be  made  in  suitable  lengths  for 
regular  underground  joints,  tinned  and  well-finished.  They  are 
usually  provided  with  an  opening  along  the  entire  length  so  as 
to  permit  of  the  solder  flowing  freely  throughout  the  joint  when 
made,  thus  insuring  a  good  soldered  union.  Both  ends  of  the 
sleeve  should  be  beveled  off,  to  remove  sharp  edges  which  would 
have  a  tendency  to  cause  a  puncture  through  the  insulation  after 
the  joint  has  been  finished.  Table  XXV  gives  the  A.  S.  &  W. 
Co.  standard  dimensions  of  copper  sleeves  for  jointing  cables. 


TABLE  XXV. — STANDARD  DIMENSIONS  OP  COPPER  SLEEVES  FOR  JOINTING 

CABLES1 


Size  of 
conductor 

Outside 
diameter  of 
Conductor,  in. 

Outside 
diameter  of 
sleeve,  in. 

Thickness 
of  copper,  in. 

Length  of 
sleeve,  in. 

Weight  per 
100  sleeves,  Ib. 

2,000,000 

1.6302 

2.168 

0.268 

6.00 

280 

1,750,000 

1.5246 

2.027 

0.251 

5.65 

242 

1,500,000 

1.4124 

1.879 

0.233 

5.30 

200 

1,250,000 

1.2892 

1.715 

0.212 

4.90 

150 

1,000,000 

1.1520 

1.532 

0.190 

4.45 

110 

900,000 

1.0935 

1.454 

0.180 

4.25 

88 

800,000 

1.0305 

1.360 

0.170 

4.05 

76 

750,000 

0.9981 

1.327 

0.162 

3.95 

67 

700,000 

0.9639 

1.282 

0.159 

3.80 

62 

600,000 

0.8928 

1.187 

0.147 

3.60 

52 

500,000 

0.8134 

1.082 

0.134 

3.35 

45 

400,000 

0.7280 

0.968 

0.120 

2.10 

36 

300,000 

0.6321 

0.841 

0.104 

2.75 

23 

250,000 

0  .  5754 

0.766 

0.095 

2.60 

16 

0000 

0.5275 

0.702 

0.087 

2.45 

14 

000 

0.4700 

0.625 

0.078 

2.25 

10 

00 

0.4180 

0.556 

0.068 

2.10 

7 

0 

0.3730 

0.496 

0.062 

1.95 

4 

1 

0.3315 

0.441 

0.055 

.80 

2 

0.2919 

0.388 

0.048 

.70 

3 

0.2601 

0.347 

0.043 

.60 

4 

0.2316 

0.308 

0.038 

.50 

5 

0.2061 

0.275 

0.034 

.40 

6 

0.1836 

0.244 

0.030 

.25 

7 

0.1635 

0.218 

0.027 

.25 

8 

0.1455 

0.194 

0.024 

.25 

9 

0.1305 

0.172 

0.022 

.25 

10 

0.1155 

0.154 

0.020 

.25 

American  Steel  &  Wire  Co. 


INSTALLATION  OF  CABLES  175 

The  removal  of  sharp  projections  of  solder  from  the  copper 
connectors  is  of  utmost  importance  in  the  case  of  high-voltage 
cables  where  sharp  points  or  edges  act  as  discharge  points  to 
induce  puncture  of  the  insulation. 

INSULATING  THE  CONDUCTOR 

After  the  conductors  have  been  connected  and  soldered 
together,  they  are  thoroughly  insulated  with  tape  of  the  same 
material  as  is  used  on  the  cable  itself,  and  to  a  thickness  some- 
what greater  than  that  of  the  cable  insulation,  as  tape  applied 
by  hand  is  never  as  compact  and  free  from  air  spaces  as  when 
put  on  by  machinery.  Where  the  insulation  is  thicker  than  the 
copper  connector,  it  should  be  tapered  down  with  a  sharp  knife 
to  the  same  thickness  as  the  connector  so  as  to  leave  no  abrupt 
edges,  and  to  allow  the  tapes,  when  applied,  to  run  evenly  from 
connectors  to  insulation  without  ridges. 

The  insulated  splice  should  be  thoroughly  boiled  out  with 
hot  insulating  compound,  which  is  usually  heated  in  a  large 
pot,  the  ordinary  plumber's  gasoline  furnace  being  used.  The 
compound  should  be  of  such  a  temperature  as  to  throw  off 
moisture  readily,  and  yet  not  hot  enough  to  ignite  a  piece  of 
heavy  paper  dipped  into  it. 

The  determination  of  the  proper  temperature  is  a  matter  of 
practice  and  is  one  of  the  many  points  in  which  an  expert's 
experience  is  of  the  utmost  value. 

A  large  pan  held  under  the  splice  serves  to  catch  the  surplus 
compound,  which  can  be  returned  to  the  pot,  reheated  and  used 
again.  A  hot  closed  pot  of  compound  should  not  be  taken  down 
into  a  manhole  unless  it  has  first  been  opened  on  the  surface  of  the 
ground  to  ascertain  that  it  is  at  the  proper  temperature.  Paraf- 
fine  especially  and,  in  a  lesser  degree,  all  insulating  compounds, 
when  unduly  heated,  will  ignite  when  poured  on  damp  insulation, 
and  the  result  may  be  to  destroy  the  cable  and  severely  burn  the 
workman. 

WIPED  SOLDER  JOINT 

The  lead  sleeve  previously  slipped  on  the  cable  is  now  brought 
into  position  so  as  to  extend  equally  over  the  lead  on  each 
cable  end,  and  the  ends  of  the  sleeve  are  dressed  down  close  to 
the  lead  of  the  cable,  care  being  exercised  to  have  the  lead  sleeve 


176     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

concentric  with  the  cable.     The  sleeve  and  the  cables  are  then 
joined  by  a  wiped  solder  joint. 

FILLING  THE  SLEEVE 

The  joint  is  next  filled  with  hot  compound,  except  in  the  case 
of  rubber-insulated  cables.  Two  holes  are  tapped  in  the  sleeve, 
hot  insulation  is  poured  slowly  in  one  hole  until  it  appears  at  the 
other,  and  then  in  each  hole  alternately  until  the  joint  is  com- 
pletely filled. 

If  any  moisture  appears  in  the  joint,  as  shown  by  frothing  of 
the  insulation,  the  compound  should  be  allowed  to  flow  freely 
out  of  one  hole  until  all  moisture  is  removed. 

The  joint  should  be  allowed  to  cool  for  a  suitable  period 
before  moving  it,  and  any  shrinkage  or  settling  of  the  insulation 
should  be  compensated  for  by  the  addition  of  more  compound. 
This  is  a  particularly  important  point  in  the  splicing  of  high- 
tension  cables,  and  should  be  carefully  watched. 

Jointing  Rubber-insulated  Cables. — The  splices  on  rubber- 
insulated  cables  differ  from  splices  on  other  forms  of  cable  only 
in  the  kind  of  tapes  used. 

The  wire  splice  is  made  precisely  as  hereinbefore  described. 
This  splice  is  then  covered  by  a  layer  or  layers  of  pure  rubber 
tape  spirally  applied  to  a  thickness  of  Y§±  to  J^2  m-  This  is 
covered  by  rubber-compound  tapes  applied  spirally  until  a  total 
thickness  slightly  greater  than  the  insulation  of  the  cable  is 
secured.  Over  all  is  placed  a  layer  of  linen  tape  thoroughly  im- 
pregnated with  rubber  to  render  it  adhesive.  The  lead  joint  is 
then  made  in  the  regular  manner,  but  is  not  filled  with  hot 
compound.  In  some  instances  it  is  necessary  to  vulcanize  thor- 
oughly the  rubber  tapes  so  as  to  cure  the  rubber  and  render  it 
homogeneous,  elastic  and  water-tight.  This  process  should  be 
entrusted  only  to  experts. 

Jointing  Armored  Cables.— When  lead-covered  cables  are 
provided  with  steel-wire  armor,  a  joint  in  the  armor  wires  is 
required  in  addition  to  the  joint  on  the  cable,  the  latter  being 
made  in  the  regular  manner.  While  making  the  lead-covered 
joint,  the  armor  wires  should  be  bound  by  tie  wire  on  either  side, 
and  bent  back  out  of  the  way.  When  the  cable  is  spliced  and 
the  lead  joint  completed,  the  cable  should  be  protected  with 
wrappings  of  jute  over  the  lead  sleeve  and  the  armor  wires,  from 


INSTALLATION  OF  CABLES  177 

one  side,  bent  down  and  spaced  uniformly  over  the  sleeve.  The 
sleeve  being  larger  than  the  original  cable,  there  will  be  space 
between  the  armor  wires,  and  these  are  filled  by  the  armor  wires 
from  the  other  side  of  the  joint,  the  two  sets  of  wires  being 
thus  interlaced.  If  there  is  not  space  enough  between  the  wires 
from  one  side  for  all  the  wires  from  the  other,  the  surplus  wires 
are  cut  off  short  on  one  section  and  the  corresponding  wires  on 
the  other  section  left  long  enough  to  butt  against  the  short  wires, 
thus  covering  the  joint  completely  and  evenly  with  the  armor 
wires.  Where  the  armor  wires  are  thus  placed,  they  are  firmly 
bound  together  by  a  tight  serving  of  wires  wound  in  a  short 
spiral  around  the  entire  length  of  the  splice  and  carefully  soldered 
to  the  armor.  A  joint  thus  made  will  be  mechanically  as  strong 
as  any  other  part  of  the  cable. 

As  the  durability  of  a  joint  is  dependent  upon  the  proper  exe- 
cution of  what  might  seem  to  be  the  most  minute  details,  a 
description  of  some  of  the  methods  of  making  up  joints  on  three- 
conductor  paper  cables  is  printed  herewith. 

Paper  and  Cambric  Tape-insulated  Joints. — The  ends  of  the 
cable  are  prepared  in  the  usual  manner  by  stripping  off  the  lead. 
The  paper  insulation  is  trimmed  away  to  expose  the  conductors. 
Split  copper  sleeves  are  slipped  over  the  conductors  that  are  to 
be  joined  and  the  sleeve  is  then  sweated  on  with  solder.  No 
acid  should  be  used  as  a  flux  in  soldering,  as  it  is  likely  to  injure 
the  insulation. 

The  insulation  on  the  conductors  on  each  side  of  the  sleeve 
should  be  cut  down  to  a  pencil  point  so  as  to  allow  the  tape  to  be 
built  up  evenly  without  butt  joints.  The  best  work  that  can 
be  done  by  hand  will  be  considerably  looser  than  the  machine- 
wrapped  insulation  on  the  main  cable,  and  for  that  reason  the 
tape  should  be  put  on  thicker  than  the  original  insulation.  In 
applying  tape  on  cables  used  for  voltages  over  10,000,  a  suitable 
compound  should  be  applied  with  a  brush  to  each  layer  of  tape. 
This  will  tend  to  prevent  the  formation  of  air  cells  which  invari- 
ably accompany  the  taping  of  a  joint  and  which  have  been  found 
to  impair  seriously  the  insulation  of  a  high- voltage  joint.  During 
the  progress  of  the  wrapping,  the  insulation  should  be  boiled  out 
thoroughly  by  pouring  hot  compound  over  the  layers  of  tape  to 
exclude  all  moisture.  Moisture  from  the  hands  of  the  splicer 
may  be  sufficient  to  destroy  an  otherwise  perfect  joint. 

After  all  conductors  are  thoroughly  taped  and  boiled  out,  a 

12 


178     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


FIG.  76. — Steps  in  making  three-conductor  paper-insulated  lead-covered 

cable  joint. 


INSTALLATION  OF  CABLES  179 

small  roll  of  tape  should  be  placed  between  the  conductors  to 
separate  them.  An  outer  wrapping  of  tape  should  be  applied, 
which  is  drawn  tight  and  wrapped  until  it  is  considerably  larger 
than  the  original  insulation  but  not  too  large  to  permit  the  lead 
sleeve  to  be  placed  over  it.  Numerous  incisions  are  then  made 
in  the  outer  wrapping  in  order  to  allow  the  compound  to  fill  up 
all  the  voids  on  the  inside.  Great  care  must  be  taken  in  punch- 
ing these  holes  not  to  injure  the  insulation  on  the  individual 
conductors. 

The  lead  sleeve  which  has  previously  been  prepared  and 
placed  over  one  of  the  cable  ends,  is  now  beaten  into  proper 
form  and  placed  evenly  over  the  joint.  The  sleeve  is  then 
soldered  to  the  cable  sheath  with  a  regular  wiped  joint.  The 
wipes  must  be  absolutely  water-tight  and  should  be  carefully 
inspected,  especially  on  the  underside  of  the  joint,  by  means 
of  a  small  mirror  to  insure  smoothness,  solidity,  and  absence  of 
air  holes.  This  is  most  important  as  the  presence  of  small  blow- 
holes is  known  to  have  caused  perhaps  more  trouble  than  any 
other  feature  in  joint  making.  The  various  steps  in  the  making 
of  a  three-conductor  high-tension  cable  joint  are  fully  illustrated 
in  Fig.  76. 

For  filling  the  joint,  two  holes  are  punched  in  the  top  of  the 
lead  sleeve  about  3  in.  from  each  end,  one  to  pour  compound 
through  and  the  other  to  serve  as  an  air  vent.  The  compound 
should  be  poured  very  hot  and  the  pouring  continued  until  the 
compound  overflows  at  the  opposite  end.  After  standing  for 
half  an  hour  or  more,  the  sleeve  is  refilled,  after  which  the 
openings  in  the  sleeve  are  sealed  by  soldering  a  small  lead  patch 
over  each. 

Paper-tube  Joints. — The  Standard  Underground  Cable  Co. 
recommend  the  following  procedure  for  making  high-voltage 
paper-tube  joints: 

Cut  off  ends  of  cable  square.  Cut  off  lead  on  one  cable  at  a 
point  approximately  6  in.  back  from  end;  and  on  the  other  cable 
approximately  9  in.  back  from  end.  (CAUTION. — The  longi- 
tudinal cut  in  lead  should  be  made  by  inserting  cutting  knife 
tangential  with  the  inside  curve  of  the  lead  sheathing.  Circum- 
ferential cut  should  be  made  by  nicking  lead  only  part  way 
through  and  then  tearing  by  pulling  it  apart  with  pliers.)  Re- 
move belt  insulation  to  a  point  about  1J^  in.  from  edge  of  lead. 
(CAUTION. — Inner  layers  of  paper  of  belt  should  be  torn  rather 


180     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

than  cut,  to  prevent  damaging  insulation  on  individual  con- 
ductors.) Pull  jute  filler  back  and  cut  off  at  point  close  to  end 
of  belt  insulation.  The  individual  conductors  will  now  be  found 
to  be  about  3  in.  longer  on  one  cable  than  the  other. 

Strip  individual  conductors  of  insulation  for  a  distance  J^  in. 
greater  than  one-half  the  length  of  the  copper  sleeve. 

Thread  lead  sleeving  over  one  of  the  abutting  ends  of  cable  and 
move  back  out  of  the  way.  Thread  large  enclosing  joint  tube, 
when  used,  back  over  cable  end  and  back  out  of  the  way.  Thread 
the  small  jointing  tubes  over  the  ends  of  the  long-length  indi- 
vidual conductors  (i.e.,  the  conductors  on  the  cable  and  whose 
lead  sheathing  was  trimmed  back  9  in.),  and  push  back  far  enough 
to  leave  copper  ends  of  conductors  easily  accessible. 

Tin  conductors  thoroughly  with  hot  solder  applied  by  ladle. 
Insert  ends  of  conductors  intended  to  be  connected  together, 
into  the  split  copper  connectors,  which  should  preferably  be  of 
such  size  that  even  when  compressed  upon  the  conductor,  the 
longitudinal  split  will  remain  open  Jf  g  or  %2  m-  With  split 
in  copper  sleeve  uppermost,  apply  hot  solder  with  a  ladle,  and 
when  thoroughly  heated,  compress  copper  tube.  Then  sweat 
tube  and  connectors  thoroughly  together,  keeping  joint  as  full 
of  solder  as  possible.  Wipe  off  all  fins  or  points  before  solder 
sets.  (CAUTION. — Do  not  file  off  fins  or  sharp  points  unless  the 
tubes  and  insulation  of  all  the  conductors  are  protected  from 
falling  particles  of  metal.  Do  not  move  the  sleeve  or  joint, 
otherwise  the  solder,  if  it  be  at  about  the  critical  temperature 
when  mealiness  appears,  may  not  unite  the  parts  satisfactorily.) 

Fill  space  between  end  of  copper  sleeves  and  insulation  on 
each  side  with  loosely  woven  and  easily  impregnated  cotton 
tape.  (For  previous  preparation  of  cotton  tape  see  below.) 
Apply  similar  tape  in  layers  over  the  copper  connector  to  a 
diameter  equal  to  the  diameter  of  the  insulated  conductor.  Boil 
out  tape  and  adjacent  cable  ends  carefully  with  insulating  com- 
pound at  a  temperature  of  about  375°F.  (CAUTION. — As  the 
tape  must  have  its  moisture  boiled  out  in  case  any  is  present, 
and  be  thoroughly  impregnated  besides,  nothing  but  very  hot 
compound  will  suffice.) 

After  all  conductors  have  thus  been  connected,  move  each  of 
the  splicing  tubes  back  to  cover  thoroughly  the  completed  joint 
on  the  conductor.  (CAUTION. — Proper  position  for  splicing  tube 
is  such  that  the  middle  of  the  tube  shall  be  over  the  middle  of 


INSTALLATION  OF  CABLES  181 

the  copper  sleeve,  or  so  that  the  tube  shall  equally  overlap  the 
original  conductor  insulation  at  each  end.)  Fasten  each  end  of 
a  piece  of  dry  cotton  tape  to  the  conductor  at  each  side  of  and 
bridging  the  tube,  thus  holding  it  permanently  in  place.  Move 
the  enclosing  or  large  splicing  tube  back  over  the  smaller  tubes 
so  that  it  occupies  a  middle  position.  Bind  in  place  with  tape 
in  a  manner  similar  to  that  just  described  for  individual  conductors. 
(CAUTION. — Do  not  put  wrappings  of  any  sort — either  paper, 
linen  or  rubber — over  the  tubes,  as  this  prevents  the  proper 
ingress  of  filling  compound  into  the  interstices  between  tubes  and 
conductors,  and  between  inner  and  outer  tubes,  a  condition  abso- 
lutely essential  to  complete  success  in  a  joint  of  this  type.) 

Move  lead  sleeving  back  into  proper  position,  i.e.,  so  that  at 
each  end  it  overlaps  equally  the  lead  sheathing  of  the  abutting 
cables.  Dress  down  ends  of  sleeves  to  fit  neatly  around  cable 
sheathing.  Wipe  joint  carefully  with  edges  of  the  wipe  at  least 
%  in.  back  from  the  line  at  which  the  lead  sheathing  and  the  lead 
sleeving  meet.  Make  two  holes,  one  at  each  end  and  on  top  of 
the  lead  sleeving.  One  of  these  is  for  admission  of  the  hot  com- 
pound, the  other  for  its  overflow.  These  holes  should  be  of  V-- 
shaped form,  and  the  one  selected  for  filling  should  be  preferably 
on  the  end  farthest  away  from  the  paper  tubes,  and  so  located 
that  the  stream  of  hot  filling  compound  will  strike  the  paper-belt 
insulation  of  the  jointed  cable.  Tilt  the  joint  slightly  so  that 
the  filling  hole  will  be  slightly  above  the  level  of  the  other  hole. 
Pour  in  filling  compound  heated  to  a  temperature  of  from  325°. 
to  350°F.  until  it  issues  from  the  other  hole; and  if  bubbles  appear, 
indicating  moisture  in  the  joint,  continue  pouring  at  upper  hole 
and  emptying  through  lower  hole  until  every  evidence  of  mois- 
ture disappears.  After  allowing  to  settle  for  %  or  %  hr.,  pour 
in  additional  compound,  after  which  seal  both  holes  carefully 
with  solder.  (CAUTION. — A  heavy  soldering  iron  properly 
heated  must  be  used  to  insure  adhesion  of  plenty  of  solder  around 
the  opening.) 

The  illustration  shown  in  Fig.  77  indicates  the  various  steps  in 
the  making  of  a  tube  joint  as  just  described. 

Advantages  of  Paper-tube  Joint. — The  following  points  of 
superiority  are  claimed  for  the  above  type  of  joint: 

(a)  Absolute  certainty  of  proper  insulation  and  separation 
between  conductors  and  between  conductors  and  lead,  the  judg- 
ment of  the  workmen  as  to  these  points  being  entirely  eliminated. 


182     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


(b)  Freedom  from  moisture,  the  tubes  being  thoroughly  im- 
pregnated with  insulation  at  the  factory  by  immersion  in  hot 
compound. 


hO 


.2 


(c)  Freedom  from  air  spaces.  The  fact  that  there  are  no  con- 
volutions of  tape  to  be  penetrated  by  the  compound  used  in 
filling  the  sleeve,  makes  it  certain  that  the  entire  joint  will  be 
thoroughly  filled. 


INSTALLATION  OF  CABLES 


183 


(d)  Ease  of  application,  with  consequent  saving  in  labor  and 
expense. 

Sleeve -filling  Material. — There  seems  to  be  a  general  impres- 
sion among  cable  users  who  have  not  carefully  investigated  the 
matter,  that  almost  any  compound  is  good  enough  for  a  cable 
joint.  Paraffine  has  met  with  general  favor  in  spite  of  its  inher- 
ent disadvantages.  Some  of  the  properties  which  are  considered 
desirable  for  a  good  jointing  compound  are: 

1.  High  melting  point. 

2.  Adhesiveness. 

3.  Not  brittle  at  ordinary  temperatures. 

4.  Resists  high-puncture  tests. 

5.  Low  coefficient  of  contraction. 


FIG.  78. — Sections  of  high-voltage  cable  joints  filled  with  different  com- 
pounds. 

Some  of  the  objections  to  the  use  of  paraffine  are:  It  does  not 
have  the  property  of  sticking  tightly  to  smooth  surfaces.  It 
becomes  extremely  fluid  at  about  125°  or  130°F.  At  the  time  of 
cooling,  paraffine  has  an  excessive  contraction  coefficient  which 
results  frequently  in  voids  which  have  a  dielectric  strength  lower 
than  ordinary  atmospheric  air. 

There  are  cases  where  very  good  results  have  been  secured  with 
compounds  of  an  inferior  grade  but  this  constitutes  no  argument 
in  favor  of  the  reduction  of  the  factor  of  safety  through  the  use 
of  such  inferior  compounds  since  the  unfavorable  conditions  for 
jointing  and  operating  underground  cables  almost  everywhere 
existent  in  cities  imperatively  demand  the  use  of  the  best  com- 
pound available. 


184     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


In  Fig.  78  are  illustrated  sections  of  actual  test  joints  on  high- 
voltage  cables.  A  and  D  are  joints  filled  with  high-grade  com- 
pound; B  and  C  with  inferior  compound  offered  for  similar  use. 
A  and  B  were  exposed  to  a  temperature  of  110°F.  for  2  hr.; 
C  and  D  to  a  temperature  of  80°  to  85°F.  for  6  weeks.  Note  the 
way  the  high-grade  compound  held  its  place  in  the  sleeve,  al- 
though it  remained  soft  and  rubbery  to  the  touch  and  showed  no 
signs  of  brittleness.  The  other  compound,  soft  enough  to  almost 
empty  the  sleeve,  was  so  brittle  that  at  85°F.  a  slight  blow  with 
a  lead  pencil  broke  the  streamers  into  fragments. 

Breakdowns  solely  attributable  to  the  use  of  inferior  insulat- 
ing compounds  or  to  good  compounds  which  are  ill  adapted  to 


FIG.  79. — Viscosity  test  of  cable-sleeve-filling  compounds. 

the  conditions  under  which  they  are  being  used,  are  of  frequent 
occurrence. 

A  high  coefficient  of  expansion  is  indeed  somewhat  objection- 
able, but  a  moderate  one  must  be  accepted  as  unavoidable,  if 
the  other  desirable  characteristics  of  a  good  insulating  compound 
are  to  be  obtained  in  anything  like  a  satisfactory  degree. 

The  necessity  for  having  compound  which  will  keep  its  place 
in  the  joint  cannot  be  overemphasized.  In  many  manholes 
the  joints  are  somewhat  higher  than  the  cables  themselves,  and 
where  compounds  with  too  light  a  base  are  used,  there  is  almost 
always  danger  of  the  compound  slowly  moving  away  from  the 
joint  into  the  abutting  cable  end,  it  being  a  peculiar  character- 
istic of  some  of  these  compounds  that  they  flow  no  matter  what 
the  temperature  is.  In  such  joints,  even  when  they  appear  very 
hard  and  brittle,  the  compound  will  be  capable  of  flowing  out 


INSTALLATION  OF  CABLES 


185 


of  extremely  small  openings,  the  rate  of  flow  being  dependent 
upon  the  pressure  and  temperature.  This  is  well  illustrated  in 
Fig.  79,  which  shows  one  compound  flowing,  even  though  it 
is  hard  and  brittle,  the  other  compound  retaining  its  elasticity 
to  a  large  degree  and  showing  almost  no  sign  of  movement. 

There  is  an  additional  reason,  however,  particularly  in  high- 
voltage  cable,  for  keeping  the  joint  full  of  compound.  If  any- 
one will  take  the  trouble  to  experiment  with  a  copper  conductor 
surrounded  with  thin  layers  of  insulating  material  and  over  which 
is  a  thin  metallic  sheath,  he  will  discover  that  when  various  vol- 
tages are  applied  (starting  with  say  1,500  volts)  between  the  con- 


CONDUCTOf? 


SHEATH 


WWWWVWVVWW1 

AAAAAAA 

FIG.  80.— Electrical  discharge  between  insulation  and  conductor  of  a  * 

cable. 

ductor  and  sheath,  there  will  appear,  when  the  experiment  is 
made  in  a  sufficiently  dark  room,  an  electric  discharge  accom- 
panied by  a  glow  of  light,  where  the  metallic  sheathing  comes 
into  contact  with  the  cable  insulation  (see  Fig.  80).  This  elec- 
trical discharge  is  of  the  corona  or  brush  type,  and  with  it  there  is 
given  off  a  considerable  quantity  of  ozone,  dependent  in  amount, 
among  other  things,  upon  the  thickness  of  insulation  which 
separates  the  conductor  and  the  sheath,  and  upon  the  voltage 
applied.  Now  this  ozone  is  being  produced  in  a  manner  very 
similar  to  that  which  has  been  adopted  so  extensively  during  the 
last  few  years  for  sterilizing  water  by  oxidation  of  its  vegetable 
and  animal  impurities.  Its  effect  upon  vegetable  insulating 
material,  such  as  paper,  fiber,  varnished  cloth,  rubber,  etc.,  is 
very  deleterious,  and  ultimate  destruction  of  the  insulation 
almost  invariably  ensues  where  it  is  exposed  to  the  action  of 


186     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

newly  produced  or  nascent  ozone  for  any  considerable  time.  So 
long  as  the  edge  of  the  sheath  and  the  neighboring  wall  of  cable 
insulation  are  thoroughly  covered  by  insulating  compound,  so 
that  air  is  excluded,  there  will  be  little  or  no  deterioration  of 
the  insulation  at  these  points. 


Jnsu/at/ng  5/eeve 
/nclos/ng  Ce//s 


fitting 
Compound 


Interlocking  Ce// 
Partition. 

FIG.  81. — Conducell  cable-joint  insulators. 

Conducell  Cable-joint  Insulators. — There  has  lately  been 
placed  on  the  market  a  new  design  of  insulating  form  for  use  in 
making  cable  joints.  These  forms  are  made  of  thin  sheets  of 
mica,  cemented  together  and  made  up  over  an  iron  form. 
The  insulators  for  the  individual  conductors  are  so  made  as  to  fit 


FIG.  82. — Cable  joint  made  with  Conducell  insulators. 

into  one  another,  as  illustrated  in  Fig.  81,  giving  a  round  outer 
surface,  over  which  the  outer  cylindrical  sleeve  is  slipped.  A 
porcelain  spacer  at  each  end  holds  the  separators  symmetrically 
about  the  three  conductors  and  centrally  in  the  lead  sleeve, 
Fig.  82. 


INSTALLATION  OF  CABLES 


187 


The  advantages  claimed  for  this  construction  are: 

1,  It  is  not  necessary  to  cut  the  insulation  back  so  far  as  when 
tubes  or  hand  wrapping  are  used,  as  the  forms  do  not  have  to 
be  slipped  back  on  the  conductors  but  can  be  put  into  position 
from  the  side  after  the  conductors  are  jointed. 

2.  The  conductors  do  not  have  to  be  bent  as  much  as  when 
hand- wrapped.     This  bending  is  apt  to  crack  the  paper  near  the 
edge  of  the  belt. 


30   40   50   60   70   80   90  100  110  120  130  Cent. 
68   86  104  122  140  158  176  194  212  230  248  266  .Eahx, 
Temperature 

FIG.  83. — Hardness  of  Conduline  compound  and  comparative  dielectric 

losses  in  cables. 

3.  The  joint  can  be  made  up  in  about  one-half  the  time 
required  to  make  a  hand-wrapped  joint. 

4.  The  material  used  possesses  very  high  dielectric  properties 
and  does  not  absorb  atmospheric  moisture  to  any  appreciable 
extent. 

Advantages  1  and  4  are  peculiar  to  the  joint  material  here 
mentioned,  while  2  and  3  would  apply  to  any  type  of  tube 
joint. 

For  the  filling  of  these  joints,  a  compound  has  been  developed 
which  is  especially  suited  to  the  purpose. 

The  curve,  Fig.  83,  illustrates  the  properties  claimed  for  the 
filling  compound  mentioned. 


188     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 
The  mica  forms  are  supplied  in  three  different  grades: 

4-in.,  No.  209  for  use  on  from  2,000  to  9,000  volts. 
4-in.,  No.  1,014  for  use  on  from  10,000  to  14,000  volts. 
5-in.,  No.  1,525  for  use  on  from  15,000  to  25,000  volts. 

Laboratory  tests  indicate  that  joints  made  up  with  the  No. 
1,014  material  break  down  at  from  90,000  to  100,000  volts  be- 
tween conductors.  On  other  tests,  joints  heated  to  70°C.  stood 
50,000  volts  2  hr.  or  more  after  a  14-hr,  preliminary  run  at 
50,000  volts  at  room  temperature. 

In  none  of  these  tests  did  the  breakdown  occur  in  the  joint 
proper,  but  all  were  in  the  cable  beyond  the  joint,  usually  under 
or  beyond  the  wipe. 

Several  companies  have  these  joints  in  service  on  8,000-  and 
15,000-volt  circuits  without  failure  and  have  adopted  the  material 
as  standard  construction  on  emergency  work  because  of  the 
reduced  time  required  to  return  feeders  to  service. 

High-voltage  Vacuum  Joint. — The  tendency  toward  centraliza- 
tion of  power  generation  has  recently  necessitated  the  operation 
of  underground  cables  at  considerably  increased  transmission 
voltages. 

While  the  cable  itself  is  so  designed  as  to  operate  satisfactorily 
at  high  voltages,  a  great  deal  of  trouble  has  been  experienced 
due  to  breakdowns  in  the  cable  joints.  The  joints  employed 
when  cables  were  first  used  to  transmit  at  voltages  higher  than 
13,000  to  15,000  were  of  essentially  the  same  type  of  construction 
as  the  joints  which  had  been  in  general  use  and  which  had  given 
satisfactory  service  at  the  lower  voltages. 

Experience  has  shown,  however,  that  joints  as  ordinarily  con- 
structed frequently  fail  at  operating  voltages  in  excess  of  15,000. 

A  series  of  high-voltage  tests  made  by  a  large  operating  com- 
pany on  joints  using  various  types  of  compound  failed  to  give 
uniform  and  satisfactory  results.  Paraffine  compounds  shrink 
during  cooling  and  leave  voids  in  the  joint  space.  High-melting- 
point  gum  compounds,  because  of  their  viscosity,  do  not  com- 
pletely fill  the  crevices  and  have  the  additional  disadvantage 
that  short-circuit  conditions  develop  cracks  in  the  compound 
which  are  not  self-healing. 

These  disadvantages  are  not  serious  enough  to  cause  much 
trouble  at  lower  voltages,  but  under  high-voltage  stresses  the 
danger  of  joint  breakdowns  is  greatly  increased. 


INSTALLATION  OF  CABLES  189 

Experiments  have  been  made  on  a  joint  insulated  with  liquid 
fillers,  such  as  rosin  or  mineral  oil,  which  are  fluid  at  low  tempera- 
tures. These  joints  gave  uniformly  good  results,  but  some  diffi- 
culty was  experienced  from  the  leaking  of  the  oil  from  the  joint 
space  along  the  cables.  This  difficulty  was  overcome  after  con- 
siderable experimenting;  and  a  very  satisfactory  high-voltage 
joint  has  been  designed  and  patented  by  Mr.  Philip  Torchio, 
chief  electrical  engineer  of  the  New  York  Edison  Co. 

In  making  this  joint  the  cutting  of  the  insulation  and  the 
application  of  new  insulation  conforms  to  a  special  gage  which 
is  part  of  the  cable-splicers'  equipment.  The  lead  sheath  is 
stripped  off  in  the  usual  way  preparatory  to  jointing.  After 
the  conductors  are  soldered,  all  metal  points  and  burrs  are  re- 
moved by  filing  and  with  emery  cloth,  and  the  space  between  the 
conductors  is  thoroughly  cleansed  of  all  particles  of  emery  and 
copper.  A  liberal  application  of  compound  is  given  to  the  con- 
ductor to  be  insulated,  and  impregnated-paper  tape  %  in.  wide 
and  3  mils  thick  is  wrapped  tightly  around  it.  Each  layer  of  tape 
receives  an  application  of  compound  before  the  next  is  applied 
and  each  turn  of  the  tape  is  drawn  tight  so  as  to  squeeze  out  any 
air  bubbles  which  might  collect  in  the  space  between  the  layers. 
The  hand-applied  insulation  at  its  thickest  point  is  about  one  and 
one-quarter  times  that  of  the  mill-applied  insulation. 

After  each  of  the  three  conductors  has  received  its  applied 
insulation,  the  space  between  the  conductors  is  filled  with  com- 
pound, and  strips  of  jute,  laid  parallel  to  the  conductors,  are 
packed  into  the  space  so  as  to  completely  fill  it;  and  the  whole  is 
then  saturated  with  compound.  The  belt  insulation  of  impreg- 
nated-paper tape,  1  in.  wide  and  6  mils  thick,  is  next  applied,  and 
the  same  general  method  of  application  is  adhered  to  as  was  used 
in  insulating  the  individual  conductors,  so  as  to  eliminate  pockets 
and  voids. 

The  finished  belt  is  pierced  in  six  places  with  the  idea  of  facili- 
tating the  removal  of  air  and  complete  impregnation  with  the 
compound,  and  is  encased  in  a  metal  sleeve,  made  of  30-mesh  No. 
30  copper  wire  gauze,  which  covers  the  joint  and  extends  about 
%  in.  under  the  belled  ends  of  the  lead  sheath.  The  metal  sleeve 
is  drawn  tight  so  as  to  bear  evenly  on  all  parts  of  the  splice,  and 
the  belled  ends  of  the  sheath  are  beaten  down  and  soldered  to  the 
gauze. 

The  use  of  this  metal  sleeve  is  important  in  that  it  establishes 


190     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


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INSTALLATION  OF  CABLES  191 

permanently  the  potential  gradient  between  the  inner  conductors 
and  ground  regardless  of  the  dielectric  material  in  the  annular 
space  between  the  sleeve  and  the  sheath. 

Over  the  gauze  sleeve  is  wound  a  cotton  wick,  1 J^  in.  wide  and 
about  %2  in.  thick.     The  middle  of  the  splice  is  covered  by  only 


FIG.  85. — Connections  of  apparatus  for  creating  vacuum  in  joint  and  filling 

with  compound. 

At  the  upper-left-hand  corner  of  the  illustration  is  a  reservoir  and  kerosene  furnace  for 
heating  compound,  to  275°F.  Attached  to  the  reservoir  is  a  thermometer  with  a 
range  of  50  deg.  to  450°F.  and  a  gage  glass  for  indicating  the  height  9f  compound 
in  the  tank.  At  the  right  is  a  3-in.  by  3.5-in.  vacuum  pump  which  is  belt-driven  by  a  90- 
volt  0.5  hp.  motor.  Attached  to  the  right-hand  end  of  the  cable-joint  sleeve  is  a  suction 
chamber  equipped  with  a  vacuum  gage.  This  chamber  is  connected  with  the  pump  by  a 
0.5-in.  flexible  spiral-metal  hose  capable  of  withstanding  more  than  29-in.  vacuum.  The 
hose  between  the  compound  reservoir  and  the  left-hand  end  of  the  splice  is  1  in.  in  diameter. 
Valves  Nos.  1,  2  and  3  are  Lunkenheimer  quick-acting  lever-type  and  valves  Nos.  4,  5,  6 
and  7  are  two-way  straight  pet  cocks. 

one  layer,  but  at  the  ends  the  covering  is  several  layers  thick,  and 
when  the  wick  is  saturated  with  compound,  these  end  layers 
act  as  a  reservoir  which  supplies  the  center  layer  with  compound 
by  capillary  attraction,  thus  keeping  the  splice  saturated  at 


192     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


all  times.  The  joint  is  then  filled  with  compound  under  high- 
vacuum  conditions.  The  various  steps  in  making  this  joint  are 
shown  in  Fig.  84. 


FIG.  86. — Joint-filling  apparatus  mounted  on  electric  vehicle. 


Fia.  87. — Apparatus  supplying  compound  to  compensate  for  absorption 

by  cable. 

Fig.  85  illustrates  an  assembly  of  the  apparatus  necessary  for 
filling  and  sealing  the  joint;  and  the  illustration  in  Fig.  86  shows 


INSTALLATION  OF  CABLES  193 

the  vacuum  machine  in  use  on  an  electric  truck.  When  tests 
show  that  there  are  no  leaks  in  the  connections  or  joints  and  at 
least  27  in.  of  vacuum  is  obtained,  the  pumping  is  continued  for 
about  15  min.  to  increase  the  vacuum  to  28  in.  or  more.  Then 
the  compound  is  allowed  to  flow  in,  after  which  the  apparatus  is 
disconnected. 

A  pressure  cup,  Fig.  87,  is  connected  to  one  of  the  splice  plugs 
and  the  compound  is  forced  through  until  it  overflows  at  the  other 
nipple,  which  is  then  capped.  The  cup  is  rilled  up  with  compound, 
the  T-handle  screwed  out  to  its  furthest  position  and  the  spring- 
actuated  piston  forces  compound  into  the  joint  space  to  compen- 
sate for  any  contraction  which  may  occur  during  cooling.  The 
pressure  cup  is  left  in  place  until  the  joint  space  is  completely 


FIG.  88. — Completed  cable  joint  with  apertures  closed  by  plugs. 


filled;  the  cup  is  then  disconnected,  the  nipple  capped,  Fig.  88, 
and  the  joint  is  ready  for  operation. 

This  method  of  joint  construction  has  been  used  on  three 
25,000-volt  feeders  of  the  United  Electric  Light  &  Power  Co.  for 
supplying  power  to  the  New  Haven  Railroad  at  the  West  Farms 
Substation. 

Unit  Packages  for  Cable-Joint  Material.1 — Considerable  advan- 
tage may  be  gained  in  putting  the  material  for  cable  joints  in 
unit  packages.  One  company  has  used  this  method  in  the  con- 
struction of  joints  for  three-conductor,  350,000-cm.,  sector-type, 
25,000-volt  cable  feeders.  Reference  to  the  special  construction 
of  this  type  of  joint  is  made  in  another  part  of  this  chapter,  but 
it  may  be  stated  here  that  each  joint  was  made  to  a  template  and 
the  necessary  material  was  delivered  on  the  job  in  cans  or  pack- 
ages, Fig.  89,  two  cans  being  used,  one  for  the  filling  compound 
and  one  for  the  paper  tape  and  other  miscellaneous  insulating 
material. 

All  of  this  insulating  material  was  prepared  at  the  cable  factory, 

1  N.E.L.A.  Underground  Committee  report,  1916, 

13 


194     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

submitted  to  29  in.  vacuum  and  impregnated  with  the  same 
compound  which  was  used  in  filling  the  joint.  The  insulating 
material  is  placed  in  the  can  in  layers  in  the  order  required  to 
make  up  the  joint,  so  that  all  of  the  material  in  each  layer  has 
to  be  used  in  its  entirety  in  each  successive  operation.  The 
illustration  shows  all  the  material  used  to  make  one  complete 
joint  of  this  type. 

Another  company  reports  the  following  practice : 

When  the  lead  sleeve  is  3  in.  or  larger  in  diameter,  this  sleeving 

is  cut  to  the  exact  length  required  for  the  joint,  wooden  end  plugs 

and  through  bolts  are  used  to  seal  the  ends,  and  the  tape,  solder, 

copper  sleeves  and  soldering  paste  are  placed  within  the  sleeve. 


FIG.  89. — Contents  of  sealed-unit  package. 

If  the  package  is  sent  out  in  advance  of  the  work,  the  ends  are 
sealed  by  dipping  in  melted  paraffine. 

When  the  sleeve  is  smaller  than  3  in.  in  diameter,  a  pasteboard 
or  sheet-metal  container  is  used  to  hold  the  lead  sleeve  and  other 
material.  The  material  is  placed  in  the  pasteboard  container  if 
it  is  to  be  used  immediately,  and  in  the  sheet-metal  container  if 
it  is  to  remain  on  the  job  a  day  or  two  before  being  used.  The 
latter  is  necessary  in  order  to  keep  the  tape  dry.  Each  package 
made  up  for  No.  6  and  No.  0  single-conductor  cable  contains 
material  for  four  joints. 

As  the  exact  quantity  of  material  required  is  sent  out  in  each 
package,  uniform  joints  are  secured.  Less  time  is  required  on  the 


INSTALLATION  OF  CABLES  195 

job  to  get  material  ready  for  the  joints  because  the  lead  sleeve 
is  cut  to  the  proper  length  and  all  material  is  in  a  form  convenient 
to  handle.  There  is  also  considerable  saving  in  the  storeroom, 
as  these  packages  can  be  made  up  during  slack  time  and  are  more 
quickly  and  easily  handled  when  delivered. 

Protection  of  Cables  in  Manholes. — In  an  underground  system 
where  cables  are  carrying  from  2,000  to  5,000  kw.,  damage  to 
such  cables  becomes  a  matter  of  serious  consequence,  and  their 
protection  from  mechanical  injury,  especially  in  manholes,  is  very 
important. 

In  order  to  prevent  trouble  on  one  cable  from  communicating 
to  the  other  cables  in  the  same  manhole,  it  is  desirable  to  cover 
the  cables  in  manholes  with  some  type  of  fireproof  covering.  The 
principal  types  of  protection  used  are  as  follows: 

1.  Concrete  shelves. 

2.  Asbestos  tape  saturated  with  silicate  of  soda. 

3.  Asbestos  tape  covered  with  a  soft-steel  band  armor. 

4.  Split-tile  duct  with  cemented  joints. 

5.  A  cement-mortar  coating  with  %  in.  rope  bond. 
Concrete  shelves  make  a  good  protection  between  cables  on 

the  several  shelves  but,  without  other  protection,  do  not  prevent 
trouble  in  one  cable  from  extending  to  others  on  the  same  shelf. 
Nor  is  it  feasible  under  ordinary  conditions  to  extend  the  shelves 
right  up  to  the  conduit  end,  so  that  with  this  scheme  of  protec- 
tion the  cables  are  ordinarily  exposed  to  damage  when  they  enter 
and  leave  the  manhole.  These  are  the  most  vulnerable  points 
in  any  scheme  of  protection,  and  are  also  the  points  at  which 
repairs  to  cables  are  the  most  awkward  and  expensive. 

In  some  cases  specially  designed  octagonal-shaped  manholes 
have  been  used,  receiving  but  two  cables  on  the  same  horizontal 
plane,  one  turning  to  the  right  and  one  to  the  left,  giving  very 
gradual  bends  and  resting  throughout  their  length  on  reinforced- 
cement  shelves  1  in.  thick.  In  the  construction  of  these  shelves 
expanded  metal  of  1  in.  mesh  is  stretched  in  forms,  into  which 
the  concrete  is  poured,  a  mixture  of  1  part  cement  to  2  of  sand 
being  used.  A  plan  and  elevation  of  a  cable  manhole  of  this 
type  is  shown  in  Fig.  90. 

The  shelves  are  removable  and  are  laid  upon  angle  irons  built 
into  the  manhole  walls.  These  barriers  protect  the  cables  from 
being  walked  upon  by  careless  workmen,  or  struck  by  ladders, 
falling  tools,  etc.  They  also  are  considered  a  protection  above 


196     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

and  below  in  case  of  severe  short-circuit  in  adjacent  conductors; 
moreover,  the  weight  of  the  cables  is  quite  uniformly  distributed, 
which  is  a  considerable  advantage  over  the  method  of  support- 
ing them  from  manhole  cable  racks.  These  shelves  cost  about  12 
to  15  cts.  per  sq.  ft.  They  need  be  manufactured  and  added 
only  as  the  multiplication  of  cables  in  the  conduit  line  warrants. 
The  several  forms  of  asbestos-tape  protection  that  have  been 
used  for  many  years  serve  to  protect  cable  from  flame  due  to  gas 


FIG.  90. — Concrete  shelves  in  manhole. 

burning  in  the  manhole  or  from  similar  flames,  but  will  not  with- 
stand the  action  of  an  arc  at  short  range.  Asbestos,  therefore, 
cannot  be  considered  a  reliable  form  of  protection  where  im- 
munity from  troubles  of  this  kind  is  desired.  The  asbestos 
coverings,  furthermore,  are  not  suitable  for  the  protection  of 
cable  sheaths  in  wet  manholes  where  stray  currents  are  in  evi- 
dence. Electrolytic  action  appears  to  be  accelerated  by  the 
presence  of  the  asbestos  wrapping,  the  cause  apparently  being 
due  to  chemical  decomposition  of  the  contents  of  the  asbestos 


INSTALLATION  OF  CABLES  197 

covering  under  conditions  which  promote  rapid  destruction  of 
cable  sheaths. 

Split  tile  laid  on  concrete  or  other  types  of  shelves  has  been 
used  by  a  number  of  companies  as  a  protective  covering.  Several 
manufacturers  make  split  tile  in  straight  sections  of  regular  length 
as  well  as  in  short,  straight  lengths  and  with  various  degrees  of 
curvature.  There  still  exists  with  this  type  of  protection  the 
difficulty  of  applying  the  protection  right  up  to  the  end  of  the 
conduit;  and  while  it  has  been  used  in  the  past  in  large  quantities, 
its  use  has  been  abandoned  in  favor  of  the  cement-mortar  cover- 
ing. Although  tile  is  fireproof  in  the  ordinary  sense,  it  will  melt 
and  flow  in  the  case  of  a  severe  electric  arc,  and  when  this  occurs, 
the  cable  is  exposed  to  the  arc  which  melted  the  tile.  The  tile 
is  also  injured  by  manhole  explosions.  It  is  difficult  to  cement 
the  joints  properly  so  that  there  are,  in  general,  a  number  of 
weak  points  in  the  covering  in  each  manhole.  In  addition,  there 
is  considerable  difficulty  in  a  crowded  manhole  in  tracing  indi- 
vidual cables  after  all  have  been  covered  with  tile.  The  prices 
demanded  by  the  tile  manufacturers  for  the  split-tile  duct  in 
straight  pieces  and  in  bends  were  of  considerable  influence  in 
the  decision  to  abandon  this  type  of  covering. 

The  cement-mortar  coating  is  not  affected  by  manhole  explo- 
sions, and  although  the  quality  of  the  concrete  and  its  strength 
may  be  seriously  affected  by  the  arc,  it  will  in  general  remain  in 
place  and  serve  as  a  protection  until  it  has  been  mechanically 
removed.  The  companies  that  have  tried  this  type  of  protection 
are  highly  impressed  with  its  value,  and  freely  recommend  its 
adoption. 

In  determining  the  type  of  protection  to  be  used,  the  heat- 
resisting  qualities  of  the  covering  are  of  more  importance  than 
the  heat-conducting  qualities.  Even  when  covered  with  the 
best  non-conductor,  the  cables  in  the  manholes  will  probably  be 
cooler  than  the  cables  in  the  conduit.  The  type  of  covering  used, 
therefore,  has  little,  if  any,  influence  on  the  carrying  capacity 
of  the  cables. 

The  cost  of  protecting  cables  by  the  several  methods  described 
will,  under  ordinary  circumstances,  range  between  20  and  30  cts. 
per  lin.  ft.  of  cable. 

Recent  tests  made  to  determine  the  relative  value  of  two 
types  of  protective  covering  for  cables  show  very  clearly  the 
marked  superiority  of  cement  mortar  as  compared  with  asbestos 


198     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


and  steel-tape  covering.  Briefly,  the  tests  showed  that  a  cable 
protected  with  cement  mortar  was  much  less  damaged  by  an  arc 
of  425  amp.  for  101  sec.  than  was  a  similar  cable  with  asbestos 
and  steel-tape  covering  by  an  arc  of  450  amp.  for  35  sec. 

An  objectionable  feature  connected  with  the  asbestos  covering 
is  the  presence  of  the  iron  banding  tape  which  may  become 
grounded  and  so  actually  involved  in  the  arc  circuit,  which  con- 
dition could  not  exist  where  the  cement  covering  is  used. 


Ci-EA/veO.  COAT/KG 
Of*  fA  tVA  r/M£  A  T 
//O'C.TOBC 


cove/?  W/TM  one 


CLOTH  i.Aff£Ot 
/MCH.   At*f>LY  SfCOffO 
COAT 
AT 


•SCHEME 


LOOK/MCZ  &OW/V  O/V  CASi-El  //V 

FIG.  91. — Method  of  fire  proofing  cables  in  manhole. 

Fig.  91  shows  the  method  of  fireproofing  cables  with  cement 
mortar.  In  applying  the  cement  mortar,  the  lead  sheath  of  the 
cable  is  first  cleaned  and  then  coated  with  paraffine  brushed  on 
evenly.  A  cover  of  cheese  cloth  is  then  applied,  over  which  the 
rope  is  wound,  spaced  about  J^-in.  centers.  The  cement  mortar 
of  a  mixture  of  1  part  Portland  cement  and  2  parts  of  clean  sharp 
sand  is  then  placed  over  the  rope  by  hand  with  leather  pad  and 
smoothed  down  with  a  trowel  to  a  thickness  of  %-in.  The 
method  of  protection  illustrated  in  Fig.  91  provides  for  asbestos 
listing  to  be  wrapped  around  the  cable  3  in.  inside  and  4  in. 
outside  the  duct.  This  plan  need  not  be  followed  when  the  space 


INSTALLATION  OF  CABLES  199 

in  the  manhole  will  allow  the  cement  covering  to  be  carried  right 
up  to  the  duct  and  so  make  the  protection  practically  continuous 
with  the  conduit. 

Cement  armor  has  been  found  to  be  of  considerable  protection 
to  cables  in  cases  where  they  might  be  accidentally  struck  by  tools, 
etc.,  and  serves  also  to  prevent  the  cables  from  being  bent  and 
twisted  by  men  not  conversant  with  the  proper  handling  of  this 
material. 

Current-carrying  Capacity  of  Cables. — The  current-carrying 
capacity  of  insulated  copper  cables  sheathed  with  lead  depends 
primarily  upon : 

(a)  The  size  and  number  of  conductors  and  their  relative 
position. 

(6)  The  ability  of  the  insulating  material  to  withstand  high 
temperatures  and  to  conduct  heat  away  from  the  copper  con- 
ductors; this  latter  being  in  turn  dependent  upon  the  kind  of 
insulation  and  its  thickness. 

(c)  The  initial  temperature  of  the  medium  surrounding  the 
cable. 

(d)  The   ability   of   the   medium   surrounding  the   cable   to 
dissipate  heat  with  small  temperature  rise. 

(e)  The  number  of  operating  cables  in  close  proximity  and 
their  relative  position. 

Where  a  number  of  insulated  conductors  are  under  the  same 
sheath,  they  are  subject  to  an  interchange  of  heat  somewhat 
similar  to  that  which  takes  place  when  a  number  of  separate 
cables  are  laid  closely  together;  and  for  that  reason  each  conductor 
of  a  multi-conductor  cable  will  have  a  smaller  current-carrying 
capacity  than  a  single-conductor  cable.  If  the  various  con- 
ductors are  separately  insulated  and  laid  together  in  the  form 
of  flat  or  round  duplex  or  triplex  cables,  their  carrying  capacity 
will  be  greater  than  if  they  are  laid  up  in  the  form  of  concentric 
cables.  Assuming  that  unity  represents  the  carrying  capacity 
of  single-conductor  cables,  the  capacity  of  multi-conductor 
cables  would  be  given  by  the  following : 

Two-conductor,  flat  or  round  form 0. 87 

Three-conductor,  triplex  form 0 . 75 

Two-conductor,  concentric  form 0.79 

Three-conductor,  concentric  form 0 . 60 

In  any  cable  the  area  from  which  heat  is  dissipated  is  pro- 
portional to  the  circumference  of  the  conductor  or  (since  the 


200     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

circumference  varies  as  the  diameter)  upon  the  diameter  of  the 
conductor,  while  the  cross-section  of  the  conductor  varies  as 
the  square  of  the  diameter.  Hence  the  size  of  conductor  varies 
much  more  rapidly  than  its  heat-radiating  surface,  and,  in  conse- 
quence, the  amperage  per  square  inch  or  circular  mil  of  copper 
section  must  be  less  for  large  size  conductors  than  for  small  in 
order  to  have  the  same  rise  of  temperature  under  the  same  con- 
ditions. The  usual  formula  for  carrying  capacity,  Current  = 

(Diam.    of    Cond.)%    •  ,  .  ,.  .    ,. 

— r—  —  >  takes  account  of  this  fact  but  not  to  a 

A  constant 

sufficient  degree,  and  we  find  that  for  cables  as  ordinarily  used 
in  underground  work,  a  more  correct  expression  is  Current  = 
(Diam.   of   Cond.)% 
A  constant 

Rubber  insulation  is  a  somewhat  better  heat  conductor  than 
dry  or  saturated  paper,  and,  therefore,  when  applied  to  the  same 
size  conductor  in  equal  thickness  will  permit  of  a  larger  current 
flowing  in  the  conductor  for  the  same  rise  of  temperature  above 
the  surrounding  air.  On  the  other  hand,  rubber  deteriorates 
much  more  rapidly  at  high  temperatures  than  does  saturated 
paper,  and  while  this  disadvantage  is  apparently  compensated 
for  up  to  about  150°F.  by  its  superior  heat-dissipating  qualities, 
at  higher  temperatures  deterioration  takes  place,  finally  becoming 
so  serious  that  the  value  of  the  material  as  an  insulating  medium 
disappears  in  a  comparatively  short  time. 

As  the  thickness  of  the  insulation  is  increased,  the  temperature 
of  the  conductor,  with  any  given  current  flowing,  gradually 
increases  and,  therefore,  the  current-carrying  capacity  is  reduced. 
This  reduction  in  capacity,  however,  is  not  very  great,  being  in 
the  ratio  of  about  93  for  1^2~m-  insulation  to  100  for  %2~m- 
insulation,  so  that  the  values  in  the  table  given  below  should  be 
slightly  decreased  when  greater  thicknesses  than  %2~m-  are  used. 

As  it  is  the  final  temperature  reached  which  really  affects  the 
carrying  capacity,  the  initial  temperature  of  the  surrounding 
medium  must  be  taken  into  account.  If,  for  instance,  the  con- 
duit system  parallels  steam  or  hot  water  mains,  the  temperature 
of  150°F.  (which  has  been  assumed  in  Table  XXVI  to  be  a 
maximum  for  safe  continuous  work  on  cables)  will  be  reached 
with  lower  values  of  current  than  would  otherwise  be  the  case; 
and  as  70°  is  the  actual  temperature  which  has  been  assumed 
to  exist  in  the  surrounding  medium  prior  to  loading  the  cables, 


INSTALLATION  OF  CABLES 


201 


any  increase  over  70°  must  be  compensated  for  by  reducing 
the  current  carried. 

• 

TABLE    XXVI. — RECOMMENDED    CURRENT    CARRYING    CAPACITIES    FOR 
CABLES  AND  WATTS  LOST  PER  FOOT* 

For  each  of  four  equally  loaded  paper-insulated  lead-covered  cables, 
installed  in  adjacent  ducts  in  the  usual  type  of  conduit  system  where  the 
initial  temperature  does  not  exceed  70°F.,  the  maximum  safe  temperature 
for  continuous  operation  being  taken  at  150°F. 

(Copyright  by  Standard  Underground  Cable  Co.) 


Size 
B.  &  S.  G. 

Safe  current, 
amp. 

Watts'  lost 
per  ft.  at 
150°F. 

Size,  cm. 

Safe  current, 
amp. 

Watts  i  lost 
per  ft.  at 
150°F. 

14 

18 

0.97 

300,000 

323 

4.22 

13 

21 

1.03 

400,000 

390 

4.61 

12 

24 

1.09 

500,000 

450 

4.91 

11 

29 

1.15 

600,000 

505 

5.16 

10 

33 

1.25 

700,000 

558 

5.36 

9 

38 

1.39 

800,000 

607 

5.56 

8 

45 

1.53 

900,000 

650 

5.71 

7 

53 

1.67 

1,000,000 

695 

5.86 

6 

64 

1.85 

1,100,000 

740 

6.01 

5 

76 

2.08 

1,200,000 

780 

6.13 

4 

91 

2.31 

1,300,000 

820 

6.25 

3 

108 

2.54 

1,400,000 

857 

6.37 

2 

125 

2.77 

1,500,000 

895 

6.49 

1 

146 

3.00 

1,600,000 

933 

6.61 

0 

168 

3.23 

1,700,000 

970 

6.73 

00 

195 

3.46 

1,800,000 

1,010 

6.85 

000 

225 

3.69 

1,900,000 

1,045 

6.97 

0000 

260 

3.92 

2,000,000 

1,085 

7.09 

*  Standard  Underground  Cable  Co. 

1  This  column  represents  the  amount  of  energy  which  is  transformed  into  heat  and  which 
must  be  dissipated.  It  is  what  is  usually  called  the  IzR  loss  and  it  is  figured  by  using  for 
I  the  current  values  given;  and  for  R  the  resistance  of  the  respective  conductor  at  a  tempera- 
ture of  150°F. 

NOTE:  The  table  is  compiled  from  a  long  series  of  tests  made  by  the  Standard  Underground 
Cable  Co.,  in  conjunction  with  the  Niagara  Falls  Power  Co. 

For  rough  calculations,  it  will  be  safe  to  use  the  following 
multipliers  to  reduce  the  current-carrying  capacity  given  in 
Table  XXVI  to  the  proper  value  for  the  corresponding  initial 
temperatures: 

Initial  temperature 70      80      90     100     110     120     130     140     150 

Multipliers 1.00  0.93  0.86  0.78  0.70  0.60  0.48  0.34  0.00 

The  formulae  and  tables  prepared  by  Mr.  H.  W.  Fisher,  and 
given  in  the  handbook  of  the  Standard  Underground  Cable  Co., 


202     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


have  been  found  to  give  excellent  satisfaction  in  practice,  and 
are  here  reproduced  through  the  courtesy  of  that  company. 

TABLE  XXVII. — EQUIVALENT  CONDUCTOR  AREAS 

Of  Single  Conductor  of  Any  Size,  from  0000  to  15,  in  a  Stated  Number 
of  Smaller  Conductors1 


B.  &  S. 
G.  No. 

In  2  con- 
ductors 

In  4  con- 
ductors 

In  8  con- 
ductors 

In  16  con- 
ductors 

In  32  con- 
ductors 

In  64  con- 
ductors 

In  2  conductors, 
one  each  of 

0000 

No.    0 

No.    3 

No.    6 

No.    9 

No.  12 

No.  15 

Nos.  00  and    1 

000 

1 

4 

7 

10 

13 

16 

Oand    2 

00 

2 

5 

8 

11 

14 

17 

land    3 

0 

1 

3 

4 

6 

7 

9 
10 

12 
13 

15 
16 

18 

2  and    4 
3  and    5 

2 
3 

5 
6 

8 
9 

11 

12 

14 
15 

17 
18 



4  and    6 
5  and    7 

4 

7 

10 

13 

16 

6  and    8 

5 

8 

11 

14 

17 

7  and    9 

6 

7 

9 
10 

12 
13 

15 
16 

18 

8  and  10 
9  and  11 

8 

11 

14 

17 

10  and  12 

9 

12 

15 

18 

11  and  13 

10 

13 

16 

12  and  14 

11 

14 

17 

13  and  15 

12 

15 

18 

14  and  16 

13 

16 

15  and  17 

14 

17 

16  and  18 

15 

18 

For  the  same  temperature  rise  more  current  can  be  carried  by  using  divided  circuits  and 
the  greater  the  number  of  divided  circuits  for  the  same  equivalent  cross-section  the  greater 
the  amount  of  current  that  can  be  carried.  See  Table  XXVI,  Carrying  Capacities. 

1  Standard  Underground  Cable  Co. 

The  temperature  which  the  insulation  of  underground  cables 
will  withstand  is  the  condition  which  limits  the  current  which 
may  be  carried,  and  it  is  extremely  important  that  this  tempera- 
ture shall  not  exceed  its  critical  value.  Within  a  limited  range 
the  temperature  increments  are  directly  proportional  to  the 
increments  of  PR,  but  a  point  will  be  reached  where  this  propor- 
tionality no  longer  exists,  and  it  will  be  found  that  the  tempera- 
ture increase  per  unit  increase  in  PR  continually  becomes  larger. 
In  the  case  of  cables  used  for  direct  current,  the  temperature 
rise  of  the  cable  (other  conditions  being  equal)  depends  solely 
upon  the  PR  loss;  and  for  low-voltage  alternating-current 
cables  this  is  approximately  true. 

However,  when  a  cable  is  used  for  carrying  alternating  current 
at  a  high  voltage,  the  heat  due  to  dielectric  hysteresis  is  added  to 


INSTALLATION  OF  CABLES 


203 


the  heat  produced  by  ohmic  resistance,  and  the  effect  is  a  lower- 
ing of  the  temperature  at  which  the  insulation  may  be  safely 
operated. 

The  operation  of  high-tension  alternating-current  cables  of 
over  10,000  volts  at  too  high  a  temperature  is  especially  dangerous 
because  the  effect  of  dielectric  losses  on  temperature  rise  is  cumu- 
lative. It  has  been  found  that  after  the  safe  temperature  has 
been  passed,  the  leakage  currents  through  the  dielectric  increase 
rapidly,  causing  increased  heating  and  facilitating  the  passage 
of  more  and  more  leakage  current.  If  this  process  continues 
unchecked,  the  failure  of  the  insulation  will  quickly  result. 

Excessive  operating  temperature,  if  continued  for  a  consider- 
able length  of  time,  has  a  deteriorating  effect  which  is  permanent 
and  which  reduces  very  materially  the  useful  life  of  a  cable. 

There  is  a  lack  of  accurate  information  such  as  would  enable 
an  operating  company  to  know  when  the  danger  point  in  cable, 
operation  is  reached.  It  is  believed  that,  because  of  this  lack  of 
information,  the  tendency,  in  underground  practice,  is  to  under- 
load rather  than  overload  the  cable  system.  When  the  magni- 

TABLB  XXVIII. — RECOMMENDED  POWER-CARRYING  CAPACITY  IN  KILO- 
WATTS  OP   DELIVERED   ENERGY1 

Three-conductor,   Three-phase  Cables 


Size  in 

V  Ull>O 

B.  &  S.  G. 

1,100 

2,200 

3,300 

4,000 

6,600 

11,000 

13,200 

22,000 

Kilowatts 

6 

92 

183 

275 

333 

549 

915 

1,098 

1,831 

5 

109 

217 

326 

395 

652 

1,087 

1,304 

2,174 

4 

130 

260 

390 

473 

781 

1,301 

1,562 

2,603 

3 

154 

309 

463 

562 

927 

1,544 

1,854 

3,089 

2 

179 

35S 

536 

650 

1,073 

1,788 

2,145 

3,575 

1 

209  ] 

418 

626 

759 

1,253 

2,088 

2,506 

4,176 

0 

240 

481 

721 

874 

1,442 

2,402 

2,884 

4,805 

00 

279 

558 

836 

1,014 

1,674 

2,788 

3,347 

5,577 

000 

322 

644 

965 

1,172 

1,931 

3,217 

3,862 

6,435 

0000 

372 

744 

1,115 

1,352 

2,231 

3,717 

4,462 

7,435 

250,000 

413 

827 

1,240 

1,503 

2,480 

4,132 

4,960 

8,264 

These  tables  are  based  on  the  recommended  current-carrying  capacity  of  cables  given  in 
Table  XXVI.  A  power  factor  =»  1,  was  used  in  the  calculation  and  hence  the  values  found 
in  the  last  table  are  correct  for  direct  currents.  For  alternating  current  the  kilowatts  given 
in  both  tables  must  be  multiplied  by  the  power  factor  of  the  delivered  load. 

1  Standard  Underground  Cable  Co. 


204     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


TABLE  XXVIII. — RECOMMENDED   POWER-CARRYING  CAPACITY  IN  KILO- 
WATTS OP  DELIVERED  ENERGY. — Continued. 

Single-conductor  Cables,  A.C.  or  D.C. 


Volts 

Size  in 

B.  &  S.  G. 

125 

250 

500 

1,100 

2,200 

3,300 

6,600 

11,000 

Kilowatts 

6 

8.0 

16.0 

32 

70 

141 

211            422            704 

5 

9.5 

19.0 

38 

84 

167 

251             502            836 

4 

11.4 

22.8 

45 

100 

200     i       300            601     |    1,001 

3 

13.5 

27.0 

54 

119 

238 

356 

713 

1,188 

2 

15.6 

31.2 

62 

138 

275 

413 

825 

1,375 

1 

18.3 

36.5 

73 

161 

321 

482 

964 

1,606 

0 

21.0 

42.0 

84 

185 

370 

554 

1,109 

1,848 

00 

24.4 

48.8 

97 

215 

429 

644 

1,287 

2,145 

000 

28.1 

56.3 

113 

248 

495 

743 

1,485 

2,475 

0000 

32.5 

65.0 

130 

286 

572 

858 

1,716 

2,860 

300,000 

40.4 

80.8 

162 

355 

711 

1,066 

2,132 

3,553 

400,000 

48.8 

97.5 

195 

429 

858 

1,287 

2,574 

4,290 

500,000 

56.3 

112.5 

225 

495 

990     j    1,485 

2,970 

4,950 

600,000 

63.1 

126.3 

253 

556 

1,111 

1,667 

3,333 

5,555 

700,000 

69.8 

139.5 

279 

614 

1,228 

1,841 

3,683 

6,138 

800,000 

75.9 

151.8 

304 

668 

1,335 

2,003 

4,006 

6,677 

900,000 

81.3 

162.5 

325 

715 

1,430 

2,145 

4,290 

7,150 

1,000,000 

86.9 

173.8 

348 

764 

1,529 

2,294 

4,587 

7,645 

1,100,000 

92.5 

185.0 

370 

814 

1,628 

2,442 

4,884 

8,140 

1,200,000 

97.5 

195.0 

390 

858 

1,716 

2,574 

5,148 

8,580 

1,400,000 

107.1 

214.3 

429 

943 

1,885 

2,828 

5,656 

9,427 

1,500,000 

111.9 

223.8 

448 

985 

1,969 

2,954 

5,907 

9,845 

1,600,000 

116.6 

233.3 

467 

1,026 

2,053 

3,079 

6,158 

10,263 

1,700,000 

121.3 

242.5 

485 

1,067 

2,134 

3,201 

6,402 

10,670 

1,800,000 

126.3 

252.5 

505 

1,111 

2,222 

3,333 

6,666 

11,110 

2,000,000 

135.6 

271.3 

543 

1,194 

2,387 

3,581 

7,161 

11,935 

tude  of  the  investment  called  for  in  this  branch  of  the  industry 
is  considered,  the  importance  of  increasing  the  carrying  capacity 
of  cables  to  the  maximum  possible  value  is  realized. 

The  current-carrying  capacity  of  rubber,  cambric  and  paper 
insulated  cables,  as  recommended  by  the  General  Electric  Co., 
is  given  in  Table  XXIX. 

The  problem  of  determining  the  proper  loading  for  under- 
ground cables  remains  to  a  large  extent  unsolved,  but  more  and 
more  attention  is  being  given  to  this  subject,  and  it  is,  therefore, 
very  desirable  that  operating  companies  and  cable  manufacturers 


INSTALLATION  OF  CABLES 


205 


work  in  conjunction  with  the  view  to  the  formulation  of  a  set  of 
standard  rules. 

TABLE  XXIX. — CURRENT-CARRYING  CAPACITY 
Rubber,  Cambric  and  Paper  Cables1 

Under  ordinary  conditions  a  cable  will  attain  about  60  per  cent,  of  its 
total  rise  in  temperature  during  the  first  hour,  30  per  cent,  during  the  second 
hour,  the  final  maximum  being  gradually  reached  during  several  following 
hours. 

Concentric  cables  will  safely  carry  about  20  per  cent,  less  current  on  each 
conductor  than  the  same  size  of  single  conductor  cable.  Four-conductor 
cables,  10  per  cent,  less  than  same  size  triple  conductor.  All  temperatures 
refer  to  temperatures  of  copper  core. 

Initial  Temperature,  20°C. 


Low  tension  cable 
single  conductor 

High  tension 
cable  three 
conductor 

Size  of  cable, 
circ.  mils 

National  electric 
code,  rubber 

Rubber,   30°C. 
rise 

Var.    cam.    or 
paper,  60°C.  rise 

Rubber  and  var. 
cam.,  30°C.  rise; 
paper,  35°C.  rise 

Amp. 

Amp. 

Amp.   on   each 
conductor 

2,000,000 

1,050 

1,400 

1,750 

1,500,000 

350 

1,200 

1,500 

1,000,000 

650 

900 

1,150 

750,000 

525 

750 

900 

500,000 

390 

550 

660 

440 

400,000 

330 

460 

560 

360 

300,000 

270 

370 

450 

290 

250,000 

235 

320 

390                          250 

200,000 

200 

270 

310 

210 

150.000 

160 

220 

260 

175 

125,000 

140 

180 

210 

140 

100,000 

120 

160 

190 

125 

80,000 

104 

140 

165 

110 

60,000 

82 

110 

130 

85 

40,000 

63 

75 

90 

60 

6  B.  &  S.  solid 

46 

50 

60 

40 

8  B.  &  S.  solid 

33                            30 

36 

24 

10  B.  &  S.  solid 

24                            20                            24 

16 

1  General  Electric  Co. 

Cooling  Duct  Lines. — The  heating  of  a  duct  line  depends  upon 
the  composition  of  the  duct  itself,  the  arrangement  of  the  ducts 
relative  to  one  another,  and  the  nature  of  the  surrounding  medium. 
Where  a  duct  line  is  of  the  multiple  type,  the  ducts  furthest 
away  from  the  heat-dissipating  surfaces  will  run  hottest,  and  the 
top  row  of  ducts  will  run  at  a  higher  temperature  than  the  lower 
rows.  Care  should,  therefore,  be  taken  in  assigning  ducts  to  the 


206     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

various  cables  that  those  cables  which  are  expected  to  carry  the 
heaviest  load  be  placed  in  the  ducts  which  can  best  dispose  of 
the  heat  generated. 

The  nature  of  the  surrounding  medium  is  of  importance  in 
determining  the  temperature  of  a  duct  line.  It  is  a  well-known 
fact  that  the  temperature  of  a  duct  of  any  given  construction 
will  vary  with  changes  in  the  character  of  the  soil  through  which 
it  runs.  Thus  a  line  may  give  no  trouble  from  overheating  where 
it  runs  through  moist  soil  but  is  very  likely  to  overheat  in  sections 
where  the  soil  is  dry  or  sandy.  Attempts  have  been  made  to 
produce  artificially  the  conditions  favorable  to  rapid  heat 
dissipation,  and  various  methods  of  cooling  overheated  duct 
lines  have  been  proposed,  but  as  yet  none  has  shown  results  which 
would  justify  general  adoption.  A  method  of  cooling  by  the 
use  of  a  porous-tile  drain  laid  in  a  trench  above  the  conduit 
line  was  described  in  detail  by  Mr.  L.  E.  Imlay  in  a  paper  pre- 
sented before  the  American  Institute  of  Electrical  Engineers  in 
February,  1915.  It  was  shown  that  the  soil  surrounding  a  buried 
conduit  containing  active  electric  cables  may  become  hot,  dry 
and  powdery,  a  condition  which  would  reduce  its  thermal  con- 
ductivity to  a  minimum.  The  addition  of  moisture  to  the  soil, 
either  from  above  or  from  below  through  a  vacant  duct,  brought 
about  a  very  distinct  reduction  in  the  temperature  of  the  cables 
as  well  as  in  the  temperature  of  the  surrounding  soil.  It  seems 
readily  possible  that  future  installations  of  heavily  loaded  con- 
ducting cables,  buried  in  conduits,  will  have  special  water-cooling 
ducts  laid  in  their  immediate  vicinity  for  the  purpose  of  keeping 
down  the  cable  temperatures.  A  noteworthy  point  brought  out 
by  the  observations  of  the  author  is  the  relatively  great  distances 
to  which  the  heat  liberated  from  active  cables  in  the  buried  con- 
duit can  appreciably  raise  the  temperature  of  the  ground.  It 
appears  that  the  temperature  of  the  soil  1  meter  below  the  surface 
was  raised  by  some  20°C.  at  a  distance  of  half  a  dozen  meters 
from  the  buried  conduit. 

The  method  employed  by  the  Niagara  Falls  Power  Co.  for 
cooling  its  underground  cables  was  to  circulate  water  through 
one  of  the  vacant  ducts  adjacent  to  the  occupied  ducts.  Later 
porous  drain  tiles  were  installed  parallel  to  and  above  the  cable 
ducts  so  that  water  flowing  through  the  tile  could  percolate 
through  the  ground  surrounding  the  cable  and  finally  be  carried 
away  through  agricultural  tile  drains  installed  below  the  ducts. 


INSTALLATION  OF  CABLES 


207 


The  approximate  temperatures  of  the  cables  were  ascertained  by 
inserting  resistance  thermometers  in  ducts  adjacent  to  the  cables 
which  were  supposed  to  be  the  source  of  heat. 

Tests  were  made  by  the  Consolidated  Gas,  Electric  Light  & 
Power  Co.  of  Baltimore  in  sections  of  their  conduit  system  where 
cable  burnouts  were  frequent.  Most  of  the  troubles  in  this 
part  of  the  insulation  were  due  to  the  high  temperature  of  the 
duct  line  during  the  summer  months.  The  soil  around  the  ducts 


FIG.  92. — Duct  temperature  before  installing  cooling  system. 

was  to  a  great  extent  dried  out  and  it  seemed  logical  to  conclude 
that  some  method  of  supplying  water  to  the  duct  line  would 
improve  conditions.  Studies  were  made  of  the  temperatures 
existing  in  the  duct  line  under  regular  operating  conditions. 
The  conduits  which  were  used  principally  for  carrying  13,000- 
volt  cables  were  laid  in  made  earth  with  some  ash.  Thermome- 
ters were  placed  in  an  idle  duct  some  distance  from  a  manhole 
and  the  observations  showed  that  the  temperatures  in  the  duct 
line  responded  to  the  variations  in  load  and  to  atmospheric 


208     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

temperatures.  The  response  to  the  changes  in  load  followed 
within  a  few  hours,  but  atmospheric  temperature  variations 
produced  no  effect  for  some  days. 

The  records  as  has  been  stated  were  taken  as  a  result  of  repeated 
cable  failures.  During  the  year  1912  there  were  15  failures; 
during  1913,  7;  and  during  1914,  19.  Nearly  all  the  troubles 
occurred  during  the  summer  months,  and  most  of  them  were 
in  the  section  of  the  duct  where  the  temperature  records  were 
observed. 


FIG.  93. — Duct  temperature  after  installing  cooling  system 


During  the  summer  of  1915,  a  sprinkler  system  was  installed 
in  the  three  sections  where  the  greatest  number  of  burnouts 
had  occurred.  The  cooling  system  consisted  of  a  %-in.  iron 
pipe  with  M4-in.  perforations  at  a  3-ft.  spacing  installed  in  a 
vacant  duct.  About  4,000  gal.  of  water  per  day  at  a  temperature 
of  about  55°F.  were  supplied  to  the  system  and  it  was  found  that 
the  duct  temperature  was  reduced  about  10°F.  Some  trouble 
appears  to  have  been  experienced  due  to  plugging  up  of  the  per- 


INSTALLATION  OF  CABLES 


209 


forations.  The  charts  shown  in  Figs.  92  and  93  show  the  tempera- 
ture conditions  before  and  after  the  sprinkler  system  was  installed. 
The  results  are  not  conclusive  and  serve  merely  to  show  the  possi- 
bilities of  this  method  of  cooling. 

In  some  instances,  transmission  cables  run  through  manholes 
containing  transformers  and  heavily  loaded  cables  both  of  which 
tend  to  raise  the  temperature  of  the  duct  line.  In  such  special 
cases  it  may  be  cheaper  to  provide  a  cooling  system  rather  than 
additional  cables  in  order  that  the  existing  cables  may  be  operated 
at  their  maximum  rating  during  the  summer  peak-load  period. 

The  radiation  of  heat  from  a  duct  line  differs  from  that  from 
other  classes  of  electrical  apparatus  around  which  the  air  is 
free  to  circulate;  therefore, 
changes  in  the  temperature  of  a 
duct  line  will  not  follow  changes 
in  load  as  closely  as  in  the  case 
of  station  apparatus,  but  instead 
will  lag  to  such  an  extent  that 
the  line  may  not  reach  its  final 
temperature  for  several  days. 
This  is  especially  true  during  cer- 
tain seasons  of  the  year  when  the 
earth  around  the  duct  line  is  dry- 
ing out. 

The  drying  out  of  the  earth  in  summer  when  the  atmospheric 
temperature  is  around  90°F.  affects  the  carrying  capacity  of 
cables  quite  materially,  since  the  maximum  copper  temperature 
at  which  it  is  safe  to  operate  high- voltage  cables  is  something 
like  150°F.  A  number  of  companies  change  the  rating  of  the 
cables  according  to  the  seasons  of  the  year.  In  one  case  where 
there  are  a  number  of  cables  in  a  duct  line  it  has  been  necessary 
to  limit  the  rating  of  the  cables  in  summer  to  about  half  the 
winter  rating. 

In  order  to  facilitate  radiation  from  cables,  duct  lines  have 
been  constructed,  as  shown  in  Fig.  94,  so  that  earth  would  be  in 
direct  contact  with  each  duct. 

Connections  to  Overhead  Lines. — In  most  primary  distri- 
bution systems  in  which  part  of  the  lines  are  underground,  there 
are  connections  made  between  the  underground  cable  and  over- 
head aerial  wires.  It  is  usual  to  run  feeders  and  important 
mains  underground  for  some  distance  from  the  station  in  large 


FIG.  94.— Method  of  separating 
ducts. 


210     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

cities  and  then  connect  with  overhead  lines  in  the  more  scattered 
area. 

Where  back-yard  and  alley  distribution  is  general,  the  main 
lines  are  placed  underground  in  streets,  and  the  local  distributing 
taps  taken  off  the  overhead  lines.  It  is  quite  frequently  neces- 
sary that  underground  lines  be  carried  across  railroads,  main 
bouleyards  and  streams.  This  class  of  distribution  was  for 
many  years  very  troublesome  because  of  the  difficulty  of  properly 
caring  for  the  cable  ends  which  are  brought  up  the  pole  to  the 
overhead  line. 

Plain  joints,  made  up  by  stripping  the  lead  back  a  few  inches 
and  covering  by  tape  and  compound,  were  succeeded  by  lead 
joints  rilled  with  compound  and  left  open  at  the  end  where  the 
live  wire  came  out.  In  some  cases  joints  were  protected  by  en- 
closing them  in  boxes.  All  of  these  various  forms  were  susceptible 
to  the  action  of  the  sun  and  rain,  and  were  sooner  or  later  located 
by  lightning  flashes,  or  potential  surges,  as  the  weak  spots  in 
.the  line. 

In  recent  years  many  of  the  large  distributing  systems  have 
been  equipped  with  potheads  or  pole  terminals  designed  to  meet 
such  conditions.  Outdoor  potheads  for  pole  connections  should 
serve  the  double  function  of  connecting  the  insulated  conductor 
of  the  underground  cable  to  the  overhead  aerial  wire,  and  of 
sealing  properly  the  end  of  the  lead-covered  cable  to  protect  the 
insulation  from  moisture.  Protection  of  the  cable  insulation 
from  moisture  requires  a  structure  which  will  not  only  prevent 
the  direct  action  of  water  in  the  form  of  rain,  snow  or  sleet,  but 
will  also  prevent  the  indirect  action  of  moisture  in  the  form  of 
fog  and  water  vapor. 

Effective  devices  of  this  kind  are  today  an  absolute  necessity 
in  every  underground  cable  system.  A  single-conductor  form 
of  terminal  is  shown  in  Fig.  95.  This  terminal  consists  essen- 
tially of  three  parts :  a  conducting  stem  (a)  which  acts  as  a  con- 
tinuation of  the  underground  cable  conductor;  an  insulator  (6); 
and  a  connecting  pin  (c)  between  the  insulator  and  lead  sheath 
(forming,  in  reality,  an  expanded  extension  to  the  lead  sheath), 
which  may  be  called  the  bell. 

The  advantages  claimed  for  this  type  of  terminal  are  as 
follows : 

1.  Protection  of  the  insulation  from  injury  by  electrostatic 
discharges,  or  by  any  deteriorating  influence,  such  as  moisture, 


INSTALLATION  OF  CABLES  211 

* 

either  held  in  suspension  in  the  air  or  in  the  form  of  rain,  snow 
or  sleet. 

2.  Separation  of,  and  efficient  insulation  of,  conductor  from 
conductor,   and   conductor  from  grounded  lead  sheath,   when 
exposed  to  usual  weather  conditions. 

3.  Connection  of  underground  conductor  with  aerial  conductor 
in  an  approximately  straight  line,  thus  avoiding  bending  heavy 
conductors  or  wasting  cable  in  goose-necks  or  rain  loops. 


FIG.  95. — Single-conductor  terminal. 

4.  Facility    in    connecting     and     disconnecting     the    aerial 
extension. 

5.  Rigid    structural    unity — the    terminal,    the    cable    con- 
ductors  and   the   lead   sheath   being   tied  together  in  a  rigid 
mechanical  union. 

6.  Ease  of  installation,  the  lead  bell  being  adaptable  to  any 
diameter  of  cable. 

7.  Connection  of  current-carrying  parts  in  an  effective  manner, 
securing  good  electrical  and  convenient  mechanical  connection 
between  the  conductors  of  the  cable  and  their  aerial  extensions. 

Another  form  of  single  conductor  terminal  is  shown  in  Fig. 
96.     This  terminal  consists  of  a  porcelain  sleeve  which,  when 


212     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


filled  with  compound,  serves  to  seal  the  end  of  the  cable  insulation 
from  moisture,  and  a  porcelain  cap  which  fits  over  the  top  and 
has  ample  overlap,  excluding  water  in  a  driving  rain  and  when 
submerged.  The  cap  carries  a  copper  plug  which  is  attached 


FIG.  96. — Single-conductor  terminal. 

to  the  outgoing  terminal.  The  tube  carries  a  recessed  member 
in  which  the  plug  seats,  and  this  member  is  soldered  to  the  cable 
conductor.  The  circuit  is  thus  opened  and  closed  by  merely 
removing  and  replacing  the  cap. 


INSTALLATION  OF  CABLES 


213 


This  type  of  pothead  is  made  in  various  forms  for  voltages  up 
to  and  including  30,000  and  with  either  wiping  sleeves,  stuffing 
boxes,  or  plain  entrances  for  the  cable.  It  has  a  very  wide  appli- 
cation to  distribution  work  and  in  many  instances  the  device  is 
used  merely  as  a  disconnector  in  place  of  a  blade  or  oil  switch. 
Because  of  its  small  unit  form,  it  permits  the  installation  of  any 
complicated  switching  arrangement 
in  a  safe,  neat  and  complete  man- 
ner. 

A  form  of  multi-conductor  ter- 
minal is  shown  in  Fig.  97.  This 
type  of  terminal  is  particularly 
suitable  for  heavy  power-trans- 
mission cables.  Some  companies 
using  multi-conductor  terminals 
made  of  iron  have  experienced 
trouble  due  to  heating  caused  by 
eddy  currents  set  up  when  the  ter- 
minal is  used  on  cables  carrying 
alternating  currents.  This  trouble, 
however,  has  been  overcome  by 
making  the  metal  forked  cap  of 
the  terminal  of  non-magnetic  ma- 
terial such  as  aluminum  or  brass. 

The  pole  shown  in  Fig.  98  is  of 
particular  interest  on  account  of 
the  considerable  number  of  13,200- 
volt,  three-conductor  cables  which 
terminate  at  this  point;  and  while 
it  may  not  be  good  practice  to 
bring  out  so  many  cables  on  one 
pole,  it  shows  what  can  be  done  when  the  conditions  require  it. 

In  all  cases  where  underground  cables  are  connected  to  over- 
head lines,  some  suitable  covering  should  be  provided  at  the  end 
of  the  lateral  pipe  to  prevent  the  entrance  of  water.  There  are 
several  devices  on  the  market  which  are  arranged  to  fit  around 
the  cable  and  slip  over  the  pipe.  A  very  satisfactory  pipe  cap 
can  be  made  of  sheet  lead  from  the  cable  sheath  which  is  formed 
into  a  bell  shape  soldered  to  the  cable  and  hammered  over  and 
around  the  pipe,  as  shown  in  Fig.  99.  Unless  the  top  of  the  pipe 


FIG.  97. — Three-conductor 
head. 


pot 


214     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


is  covered,  water  will  enter  during  rain  storms,  and  in  winter 
weather  will  freeze  and  damage  the  cable. 

The    National    Electric   Light    Association    line-construction 
specification  for  joint  use  of  poles  provides  that  connection  to 


FIG.  98. — Terminal  pole. 

electric-light  lines  for  supplying  service,  or  for  street  lamps,  trans- 
formers, fuses,  switches  or  lightning  arresters  or  connections 
to  underground  wires  and,  in  general,  connections  forming  a 


INSTALLATION  OF  CABLES 


215 


part  of  the  electric-light  system  may  be  run  vertically  upon  a 
pole,  and,  if  necessary,  through  telephone  wires,  provided  such 
electric-light  wires  and  connections  are  so  constructed,  placed 
and  maintained  as  to  conform  to  the  following  requirements: 

Lead-sheathed  cable  shall  be  inclosed  within  a  pipe  or  conduit 
of  solid  insulating  material  wherever  such  cable  shall  be  run  upon 


Cement 
i  pound 


SKETCH  A 

Cable  Moulding 

D  Diameter  Depends  on 

Size  of  Cable  Installed 


Cable  Protected 
with  Wood  Moulding 
See  Detail  A 


Bell 

Cotton  Waste 
Packing 


Lead  Wipe 
Lead  Bell 


To  Manho 


FIG.  99. — Terminal  pole,  showing  methods  of  protecting  cable. 

the  pole  between  a  point  not  less  than  40  in.  above  the  highest 
telephone  wire,  connection  or  attachment,  and  a  point  not  less 
than   6    ft.    below   the   lowest   telephone   wire,    connection   or 
attachment. 
Ground  wires  or  wires  throughout  the  entire  length  of  attach- 


216     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

ment  to  the  pole  shall  be  inclosed  within  an  insulating  conduit, 
or  otherwise  effectually  insulated  and  protected.  All  cables, 
wires,  connections  and  conduits  forming  a  part  of  the  electric- 
light  system  and  carried  vertically  upon  a  pole  within  the  terms 
of  this  article  shall  be  placed  upon  the  same  circumference  of  the 
pole  on  the  crossarm  side  or  face  of  the  pole,  it  being  further 
provided  that  the  poles  jointly  used  and  having  such  vertical 
attachment  shall  be  furnished  with  pole  steps  and  that  no  vertical 
attachment  shall  be  so  placed  as  to  interfere  with  the  use  of  pole 
steps.  Where  vertical  attachments  of  the  lighting  company  pass 
telephone  crossarms,  they  shall  be  run  behind  the  telephone  cross- 
arm  and  not  across  the  face  of  such  arms. 

Lightning  Arresters. — Where  underground  cables  connect  with 
overhead  wires,  protection  of  cables  against  lightning  is  necessary; 
and  suitable  arresters  and  fuses  should  be  installed  for  this 
purpose  as  well  as  to  protect  the  station  apparatus.  Resonance 
invariably  produces  high  potentials  at  the  junction  of  overhead 
and  underground  lines,  and  these  potentials  are  often  of  sufficient 
value  to  break  down  the  insulation  of  the  cables  and  also  the 
insulation  of  apparatus  installed  on  the  system. 

Whenever  lines  contain  both  inductance  and  capacity  in  ap- 
preciable amounts,  high  voltages,  which  endanger  the  insulation 
of  the  whole  system  and  which  it  is  impossible  to  detect  on 
ordinary  switchboard  instruments,  may  exist.  Abnormal  vol- 
tages are,  therefore,  often  found  in  circuits  containing  a  com- 
bination of  underground  and  overhead  circuits. 

It  is  difficult,  however,  to  determine  the  proper  arresters  for 
such  circuits  on  account  of  the  various  conditions  to  be  met. 
Where  it  is  necessary  to  install  lightning  arresters,  the  acces- 
sibility, ease  of  inspection,  voltage  and  power  of  the  system,  as 
well  as  the  length  of  underground  and  overhead  lines,  will  be 
important  factors  in  the  selection  of  a  proper  type.  In  all  light- 
ning-arrester installations  it  is  of  the  utmost  importance  to  make 
proper  ground  connections,  as  many  lightning-arrester  troubles 
can  be  traced  to  bad  grounds. 

For  grounding  pole  arresters,  one  or  two  1-in.  or  lj^-m-  iron 
pipes  should  be  driven  into  the  ground  at  the  base  of  the  pole 
and  connected  to  the  arrester  by  means  of  a  copper  wire  not  less 
than  No.  2.  The  ground  wire  should  be  protected  for  some 
distance  up  the  pole  to  prevent  its  being  injured.  The  pipes 


INSTALLATION  OF  CABLES  217 

should  be  driven  far  enough  from  the  pole  so  that  movement  of 
the  pole  will  not  loosen  them. 

Splicing  Equipment,  Tools  and  Safety  Devices. — In  the  laying, 
splicing  and  connecting  of  cables,  certain  tools  and  accessories 
are  necessary  and  useful;  and  every  cable  splicer  should  be  sup- 
plied with  a  kit  of  tools,  as  follows: 

Gasoline  furnace.  10-in.  flat  file. 

Solder  pot  and  ladle.  10-in.  round  file. 

3-  or  4-lb.  soldering  iron.  Hacksaw  frame  and  blades. 

8-in.  side-cutting  pliers.  Wiping  cloths. 

Gas  pliers.  Kettle  for  compound. 

Chipping  knife.  Small  and  large  pan. 

Pein  hammer.  Mason's  bag. 

As  a  great  many  accidents  of  a  minor  character  are  constantly 
occurring  due  to  methods  employed  in  raising  and  lowering  tools 
and  material  from  manholes,  these  accidents  occurring  princi- 
pally from  want  of  particular  kinds  of  devices  to  prevent  the 
spilling  of  solder  and  the  tipping  over  of  tool  and  material  pans, 
the  following  tools  or  devices  which  have  been  found  very  effec- 
tive are  suggested  for  use.1 

(a)  A  very  effective  and  useful  rope  for  lowering  the  solder 
pot,  compound  kettle,  tool  pan,  etc.,  consists  of  a  small  hemp 
rope  on  one  end  of  which  is  fastened  a  snap  hook  for  engaging 
in  the  handles  or  bails  on  the  compound  kettle  and  solder  pot. 
On  the  other  end  of  this  rope  there  is  a  "sister-hook"  which  is 
useful  in  forming  a  loop  or  safety  belt  which  may  be  used  in 
emergency  cases,  Fig.  100. 

The  sister-hook,  as  shown  in  the  figure,  consists  of  two  separate 
hooks  turned  in  opposite  directions.  The  flat  sides  fit  snugly 
together,  forming  a  complete  ring  about  the  bail  of  a  kettle,  or 
anything  which  is  placed  within  the  hook,  and  make  it  prac- 
tically impossible  to  jolt  it  out  accidentally.  The  iron  rod  at  the 
other  end  is  used  when  lowering  hot  solder  pots  or  anything  which 
may  burn  or  cut  the  rope. 

(6)  A  solder  pot  which  has  eliminated  many  accidents  due 
to  the  spilling  of  solder  is  provided  with  a  flange  on  the  inside 
which  allows  the  pot  to  be  tipped  at  a  considerable  angle  with- 
out spilling  the  contents.  This  pot  also  has  a  ring  turned  in 
the  handle  which  prevents  it  from  losing  its  balance  by  the 
handle  slipping  in  the  hook  of  the  lowering  rope. 

1  N.E.L.A.  Underground  Report,  1915. 


218     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

(c)  The  compound  kettle  may  also  have  a  ring  turned  in  the 
handle  to  prevent  slipping  in  the  lowering  hook  and  consequent 
spilling  of  the  contents  on  the  workmen  below. 

(d)  A  great  deal  of  trouble  has  been  experienced  by  the  use  of 
the  ordinary  baking  pan  as  a  means  for  lowering  into  the  man- 
hole small  tools,  tape,  etc.,  which  are  commonly  used  on  cable- 
splicing  work.     To  prevent  the  pan  from  tipping  over,  handles 
may  be  put  on  each  corner  of  the  pan  and  joined  together  in  the 


FIG.  100. — Tool  lowering  rope. 

center,  forming  a  ring  in  which  the  snap  hook  on  the  lowering 
line  engages.  This  form  of  handle  for  the  material  pan  will 
always  keep  the  pan  in  balance  and  prevent  spilling  the  contents. 
(e)  An  effective  cable-sheath  knife  has  recently  come  into  use. 
This  knife  is  very  much  the  same  as  the  sheath  knife  formerly 
used,  except  for  the  provision  of  a  fiber  shield  on  each  side  of  the 
blade.  These  shields  are  set  back  just  far  enough  from  the  cut- 


INSTALLATION  OF  CABLES  219 

ting  edge  to  permit  the  sharp  edge  of  the  knife  to  penetrate  the 
lead  sheath  only,  without  cutting  the  insulation  beneath. 

(/)  A  new  type  of  cable-sheath  cutter  for  cutting  around  the 
cable  has  recently  been  introduced.  It  has  proved  very  effec- 
tive and  where  used  has  reduced  the  number  of  short-circuits 
due  to  the  old  style  of  cutting  wheel,  which  cut  through  both 
lead  sheath  and  insulation.  This  cutter  is  of  the  plier  type,  the 
cutting  blades  being  mounted  on  the  sides  of  the  plier  jaws 
extending  only  far  enough  beyond  the  inside  edge  of  the  jaws  to 
allow  the  cutter  to  cut  through  the  lead  sheath  without  disturbing 
the  insulation  beneath. 

(g)  Hacksaw  frames  used  on  cable  work  may  be  insulated  in 
several  different  ways,  one  of  which  is  to  wind  the  metal  parts 


FIG.  101. — Hacksaw  frame. 

of  the  frame  with  insulating  tape.  Another  method  is  to  have  the 
metal  parts  covered  with  rubber  and  vulcanized.  A  very  satis- 
factory form  of  hacksaw  frame  is  one  made  entirely  of  fiber, 
Fig.  101.  The  all-fiber  hacksaw  frame  has  been  used  by  one  of 
the  larger  companies  for  some  time  and  has  proved  very 
satisfactory. 

(h)  To  prevent  the  many  short-circuits  which  occur  by  junc- 
tion-box catch  nuts  and  bolts  falling  across  terminals  of  opposite 
polarity,  insulated  wrenches  may  be  used  with  good  effect. 
These  wrenches  are  of  the  socket  type  and  have  a  setscrew  with 
a  fiber  head  which  may  be  tightened  on  the  nut  of  screw  bolt 
which  is  to  be  removed.  This  holds  the  nut  or  bolt  tightly  in 
the  head  of  the  wrench  and  permits  its  safe  removal  from  the 
junction  box.  Another  very  successful  form  of  wrench  for  remov- 
ing junction-box  catch  nuts  and  bolts  is  one  in  which  the  nut  or 
bolt  head  is  held  tightly  in  the  wrench  by  a  set  of  springs. 

(i).  For  removing  the  compound  in  low-voltage  service  boxes, 


220     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

a  hard-fiber  chisel  has  been  found  very  effective  and  should  form 
part  of  the  equipment  of  every  service  wagon. 

(/)  The  ship-auger  type  of  socket  wrench  for  removing  the 
nuts  on  the  inside  cover  of  junction  boxes  is  a  very  satisfactory 
tool,  as  it  permits  the  workman  to  tighten  the  nuts  or  bolts  in 
a  very  easy  position,  and  it  also  allows  him  to  be  on  his  guard 
against  being  struck  by  vehicles  or  pedestrians. 

TOOLS  FOR  HANDLING  FUSES  AND  CATCHES 

(a)  The  use  of  wooden  pliers  in  handling  fuses  has  eliminated 
a  great  many  accidents  which  occur  from  the  careless  handling 
of  fuses. 

(6)  A  safe  and  useful  tool  for  removing  catches  in  junction 
boxes  under  short-circuit  conditions  consists  of  a  long  insulated 


FIG.  102. — Furnace  shield. 

handle  with  a  clamp  and  setscrew  on  the  end  for  holding  the 
catch.  By  using  this  device  the  workman  may  stand  some 
distance  from  the  catch  when  it  is  withdrawn. 

(c)  A  useful  instrument  for  tracing  the  cause  of  blown  fuses 
consists  of  an  insulated  handle  on  which  is  mounted  a  fuse  wire. 
This  fuse  wire  bridges  the  fuse  terminals,  and  by  blowing  indi- 
cates which  of  the  wires  of  the  circuit  is  short-circuited  or 
grounded. 

FURNACES  AND  ACCESSORIES 

(a)  Kerosene  furnaces  for  melting  solder  and  compound,  and 
for  the  heating  of  soldering  irons,  are  recommended  in  place 


INSTALLATION  OF  CABLES  221 

of  the  gasoline  furnace  which  has  caused  many  accidents  on  ac- 
count of  the  inflammability  of  the  gasoline.  To  prevent  furnaces 
from  tipping  over,  it  is  the  practice  of  some  of  the  companies  to 
fill  the  bottom  of  the  furnace  with  lead,  giving  it  a  heavy  base. 

(6)  A  very  efficient  device  which  allows  the  compound  kettle 
to  be  heated  at  the  same  time  the  solder  pot  is  on  the  furnace, 
consists  of  a  shield  which  envelops  the  solder  pot  and  carries  the 
compound  kettle  on  top  at  the  same  time.  A  hole  may  be  cut 
in  the  side  of  the  shield  in  which  a  soldering  iron  may  be  heated. 
Many  of  these  shields  are  now  in  use  with  very  satisfactory 
results,  Fig.  102. 

(c)  When  it  is  necessary  to  use  gasoline,  a  very  safe  can  or 
container  is  one  that  cannot  be  exploded  by  igniting  the  gasoline 
at  the  filling  hole.  A  can  of  this  type  is  on  the  market  in  several 
different  styles  and  thicknesses  of  material. 

TEST  LAMPS 

Several  styles  of  test  lamps  are  in  use. 

(a)  In  one  of  these  the  lamps  are  enclosed  in  a  small  wooden 
frame  which  prevents  the  lamps  from  being  broken  and  is  easily 
packed  in  the  tool  kit.  The  contact  points  in  connection  with 
this  type  of  test  lamp  are  made  of  common  brad  awls,  the  wires 
being  soldered  to  the  awl  points  at  the  wooden  handles,  forming 
not  only  an  insulated  handle  but  at  the  same  time  allowing  the 
workmen  a  firm  grip  on  the  contact  points  which  is  much  more 
desirable  than  having  loose  and  flabby  wires  in  his  hand. 

(&)  Another  form  of  test  lamp  has  metal  guards,  but  this  is 
found  to  be  undesirable  on  account  of  the  number  of  short- 
circuits  that  have  occurred  by  these  guards  falling  across  live 
wires. 

OPENING  AND  GUARDING  MANHOLES 

(a)  Hooks  for  removing  and  replacing  manhole  covers,  which 
engage  in  a  hole  in  the  manhole  cover,  are  found  to  be  very  con- 
venient. On  the  end  opposite  the  hook  there  is  a  ring  handle. 
In  using  these  hooks  the  covers  are  dragged  from  the  manhole, 
which  is  preferable  to  prying  them  up  and  turning  them  over  by 
hand,  as  this  method  frequently  results  in  injury  to  the  hands 
and  feet  on  account  of  the  covers  slipping  or  falling. 

(6)  A  guard  rail  may  be  made  either  of  pipe,  Fig.  103,  or  angle 


222     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


FIG.  103. — Wrought-iron  pipe  manhole  guard. 


FIG.  104. — Warning  flag. 


INSTALLATION  OF  CABLES  223 

iron,  both  forms  of  which  are  used  extensively.  The  guard  rail 
should  be  made  collapsible  so  that  it  may  be  stored  in  a  tool  cart 
or  wagon. 

(c)  It  is  customary  to  have  a  red  flag  displayed,  and  it  seems 
advisable  to  have,  as  a  further  safeguard,  a  danger  sign,  as  in 
many  places  very  little  attention  is  paid  to  a  red  flag.     A  flag 
which  is  kept  extended  at  all  times  by  a  wire  device  which  folds 
back  against  the  staff  when  the  flag  is  furled  is  shown  in  Fig.  104. 

(d)  Several  types  of  gratings  are  used  to  cover  open  manholes. 
Covers  made  of  flat  bar  iron  or  heavy  wire  mesh  are  commonly 


FIG.  105. — Manhole  grating. 

used.  An  excellent  type  of  grating  is  one  which  is  hinged  in  the 
center,  allowing  one  side  of  the  grating  to  be  raised  for  lowering 
tools  and  materials  into  the  manhole,  as  shown  in  Fig.  105. 
Gratings  for  manholes  are  especially  useful  near  railroad  tracks 
and  places  where  the  regular  manhole  railing  cannot  be  kept  in 
place. 

TESTING  FOR  LIVE  CABLES 

(a)  There  are  several  devices  for  testing  cables  to  determine 
whether  they  are  alive  before  working  on  them.  The  first  is  a 
pointed  tool  on  the  end  of  an  insulated  handle.  The  tool  is 
provided  with  a  short  piece  of  cable  and  clamp  for  attaching  to 
the  cable  sheath,  Fig.  106.  This  insures  the  passage  of  the  cur- 


224     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


FIG.  106.— Tool  for  testing  cable. 


FIG.  107. — Geissler  tube. 


INSTALLATION  OF  CABLES  225 

rent  through  to  ground  if  the  cable  is  alive  when  the  tool  is  driven 
into  it. 

(b)  A  similar  device,  but  of  different  form,  is  the  spear  type 
which,  on  account  of  the  length  of  the  handle,  may  be  driven  into 
the  cable  from  the  street  surface. 

(c)  Another  method  for  determining  the  cable  to  be  worked  on 
is  to  put  a  current  of  high  frequency  through  the  cable,  and  this 
cable  may  be  readily  detected  in  the  manhole  by  the  use  of  an 
exploring   coil  and  telephone   headpiece.     The  high-frequency 
note  that  is  struck  when  the  exploring  coil  comes  into  contact 
with  the  high-frequency  cable  is  readily  distinguished  from  the 
note  of  the  cables  of  lower  frequency. 

(d)  The  electroscope  is  sometimes  used  for  detecting  the  pres- 
ence of  a  live  conductor.     The  electroscope  is  used  by  high-ten- 
sion cable  splicers  to  test  a  line  after  the  lead  sheath  has  been 
removed. 

(e)  Recently  the  Geissler  tube  has  been  used  for  work  of  this 
kind.     The  tube  is  connected  between  conductor  and  ground, 
and  if  the  cable  is  alive  it  is  denoted  by  the  illumination  given 
off  by  the  tube,  Fig.  107. 

VENTILATION  OF  MANHOLES 

(a)  The  most  effective  method  of  ventilating  manholes  con- 
taining illuminating  or  other  gases  is  by  the  use  of  either  a  motor- 
driven  fan  or  one  operated  by  hand. 

(6)  There  is  another  very  efficient  device  for  ventilating  man- 
holes which,  however,  is  not  recommended  for  removing  gases. 
This  device  consists  of  a  canvas  shield  hung  on  the  handrail 
and  passing  down  to  a  point  near  the  bottom  of  the  hole.  This 
canvas  is  always  placed  facing  the  wind,  which  passes  down  in 
front  of  it  and  comes  out  of  the  hole  on  the  opposite  side  of  the 
shield.  This  device  has  been  found  to  give  entire  satisfaction 
and  is  highly  recommended  for  this  work. 

MISCELLANEOUS 

(a)  A  very  effective  lamp  guard  made  of  fiber  is  found  useful 
around  live  low-tension  work,  as  it  eliminates  the  danger  of 
short-circuits  should  the  lamp  fall  from  the  man's  hand  upon  a 
live  terminal. 

15 


226      UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

(b)  Smoke  helmets  and  respirators  are  very  useful  in  man- 
holes that  are  full  of  gas.     There  are  several  satisfactory  respira- 
tors in  use  today.     Some  of  the  less  complicated  types  of  smoke 
helmets  are  very  effective  for  rescue  work  in  manholes,  as  it  is 
possible  to  wear  them  for  periods  of  30  min.  or  more  without 
the  operator  suffering  any  inconvenience. 

(c)  Storage-battery  lamps  for  illumination  of  manholes  should 
be  used  when  current  from  the  mains  is  not  available.     The  use 
of  open-flame  lamps  or  torches  should  be  avoided. 

(d)  On  account  of  the  many  cases  of  employees  getting  dirt  in 
their  eyes,  and  receiving  other  injuries  to  their  eyes  while  working 
in  manholes,  the  wearing  of  an  approved  type  of  safety  goggle  is 
advisable. 

(e)  It  is  good  practice  to  display  red  lamps  upon  piles   of 
material  and  around  openings  at  night  and  also  on  dark  days,  as 
a  great  many  accidents  have  been  caused  by  employees   and 
others  stumbling  over  material  in  dark  places  and  also  falling 
through  unprotected  openings. 

(/)  Emergency  wagons  equipped  with  smoke  helmets,  pul- 
motors,  and  first-aid  outfits,  along  with  tools  for  quick  repairs, 
etc.,  have  proven  very  efficient. 

(g)  To  prevent  short-circuits  between  conductors  of  Edison 
tube  joints  and  prevent  undue  heating  of  conductors  adjacent 
to  the  one  being  worked  on,  the  use  of  sheets  of  asbestos  between 
conductors  has  met  with  considerable  favor. 

(h)  The  use  of  rubber  mats  in  manholes  and  junction  boxes 
has  recently  come  into  use.  By  their  use  the  cable  to  be  worked 
on  can  be  isolated,  and  the  workman  does  not  need  to  be  as  careful 
as  formerly,  not  having  to  consider  burning  the  sheaths  of  the 
adjoining  cables  while  using  solder;  and,  furthermore,  the  pos- 
sibility of  live  cable  ends  falling  on  the  other  cable  sheaths  is 
eliminated,  the  rubber  shield  completely  blanketing  all  cables 
with  the  exception  of  the  one  being  worked  on. 


CHAPTER  VII 
TESTING  OF  CABLES 

International  Electrical  Units. — The  following  resolutions  were 
adopted  by  the  International  Congress  of  Electricians,  held  at 
Chicago  in  1893.  They  were  legalized  by  act  of  Congress  and 
approved  by  the  president  on  July  12,  1894,  and  are  now  recog- 
nized as  the  International  Units  of  value  for  their  respective 
purposes. 

Resolved,  That  the  several  governments  represented  by  the 
delegates  of  the  International  Congress  of  Electricians  be,  and 
they  are  hereby,  recommended  to  formally  adopt  as  legal  units 
of  electrical  measure  the  following: 

1.  As  a  unit  of  resistance,  the  International  Ohm,  which  is 
based  upon  the  ohm  equal  to   109  units  of  resistance  of  the 
c.g.s.  system  of  electromagnetic  units,  and  is  represented  by  the 
resistance  offered  to  an  unvarying  electric  current  by  a  column  of 
mercury  at  a  temperature  of  melting  ice,  14.4521  grams  in  mass, 
of  a  constant  cross-sectional  area,  and  of  the  length  106.3  cm. 

2.  As  a  unit  of  current,  the  International  Ampere,  which  is 
one-tenth  of  the  unit  of  current  of  the  c.g.s.  system  of  electro- 
magnetic units,  and  which  is  represented  sufficiently  well  for 
practical  use  by  the   unvarying   current   which,  when   passed 
through  a  solution  of  nitrate  of  silver  in  water,  in  accordance 
with  the  accompanying  specification  (A)  deposits  silver  at  the 
rate  of  0.001118  gram  per  second. 

3.  As  a  unit  of  electromotive  force,  the  International  Volt, 
which  is  the  e.m.f.  that,  steadily  applied  to  a  conductor  whose 
resistance  is  one  International  Ohm,  will  produce  a  current  of 
one  International  Ampere,  and  which  is  represented  sufficiently 

1  000 
well  for  practical  use  by  T^TOT  of  the  e.m.f.  between  the  poles 

or  electrodes  of  the  voltaic  cell,  known  as  Clark's  cell,  at  a 
temperature  of  15°C.,  and  prepared  in  the  manner  described 
in  the  accompanying  specification  (B). 

4.  As  the  unit  of  quantity,  the  International  Coulomb,  which 

227 


228     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

is  the  quantity  of  electricity  transferred  by  current  of  one 
International  Ampere  in  one  second. 

5.  As  the  unit  of  capacity,  the  International  Farad,  which  is 
the  capacity  of  a  conductor  charged  to  a  potential  of  one  Inter- 
national Volt  by  one  International  Coulomb  of  electricity. 

6.  As  the  unit  of  work,  the  joule,  which  is  107  units  of  work 
in  the  c.g.s.  system,  and  which  is  represented  sufficiently  well  for 
practical  use  by  the  energy  expended  in  one  second  by  an  Inter- 
national Ampere  in  an  International  Ohm. 

7.  As  the  unit  of  power,  the  watt,  which  is  equal  to  107  units 
of  power  in  the  c.g.s.  system,  and  which  is  represented  sufficiently 
well  for  practical  use,  by  the  work  done  at  the  rate  of  one  joule 
per  second. 

8.  As  the  unit  of  induction,  the  henry,  which  is  the  induction 
in  the  circuit  when  the  e.m.f.  induced  in  this  circuit  is  one  Inter- 
national Volt,  while  the  inducing  current  varies  at  the  rate  of 
one  International  Ampere  per  second. 

NOTE. — Specifications  (A)  and  (B),  omitted  here,  may  be 
found  in  the  original  publication  and  in  the  electrical  handbooks. 

Standardization  Rules. — In  the  Standardization  Rules  of  the 
American  Institute  of  Electrical  Engineers,  approved  June  30, 
1915,  the  following  recommendations  are  made  in  regard  to 
cable  tests: 

HEATING  AND  TEMPERATURE  OF  CABLES 

677.  Maximum  Safe  Limiting  Temperatures. — The  maximum 
safe  limiting  temperature  in  degrees  C.  at  the  surface  of  the 
conductor  in  a  cable  shall  be: 

For  impregnated-paper  insulation (85-E) 

For  varnished-cambric  insulation (75-E) 

For  rubber  insulation (60-0.251?) . 

Where  E  represents  the  r.m.s.  operating  e.m.f.  in  kilovolts  be- 
tween conductors. 

Thus,  at  a  working  pressure  of  3.3  kv.,  the  maximum  safe 
limiting  temperature  at  the  surface  of  the  conductor  or  conduct- 
ors, in  a  cable  would  be: 

For  impregnated-paper  insulation (81.7°C.) 

For  varnished-cambric  insulation (71.7°C.) 

For  rubber  insulation (59.2°C.) 


TESTING  OF  CABLES  229 

ELECTRICAL  TESTS. 

678.  Lengths  Tested. — Electrical  tests  of  insulation  on  wires  and 
cables  shall  be  made  on  the  entire  lengths  to  be  shipped. 

679.  Immersion  in  Water. — Electrical  tests  on  insulated  con- 
ductors not  enclosed  in  a  lead  sheath,  shall  be  made  while  im- 
mersed in  water  after  an  immersion  of  12  hr.,  if  insulated  with 
rubber   compounds,   or  if  insulated   with  varnished   cambric. 
It  is  not  necessary  to  immerse  in  water  insulated  conductors 
enclosed  in  a  lead  sheath. 

In  multiple-conductor  cables,  without  waterproof  overall 
jacket  of  insulation,  no  immersion  tests  should  be  made  on 
finished  cables,  but  only  on  the  individual  conductors  before 
assembling. 

680.  Dielectric-strength  Tests. — Object  of  Tests. — Dielectric  tests 
are  intended  to  detect  weak  spots  in  the  insulation  and  to  de- 
termine whether  the  dielectric  strength  of  the  insulation  is 
sufficient  for  enabling  it  to  withstand  the  voltage  to  which  it  is 
likely  to  be  subjected  in  service,  with  a  suitable  factor  of 
assurance. 

The  initially  applied  voltage  must  not  be  greater  than  the 
working  voltage,  and  the  rate  of  increase  shall  not  be  over  100 
per  cent,  in  10  sec. 

681.  Factor  of  Assurance. — The  factor  of  assurance  of  wire  or 
cable  insulation  shall  be  the  ratio  of  the  voltage  at  which  it  is 
tested  to  that  at  which  it  is  used. 

682.  Test  Voltage. — The  dielectric  strength  of  wire  and  cable 
insulation  shall  be  tested  at  the  factory,  by  applying  an  alter- 
nating test  voltage  between  the  conductor  and  sheath  or  water. 

683.  The  magnitude  and  duration  of  the  test  voltage  should  depend 
on  the  dielectric  strength  and  thickness  of  the  insulation,  the 
length  and  diameter  of  the  wire  or  cable,  and  the  assurance  factor 
required,  the  latter  in  turn  depending  upon  the  importance  of 
the  service  in  which  the  wire  or  cable  is  employed. 

684.  The  following  test  voltages  shall  apply  unless  a  departure 
is  considered  necessary,  in  view  of  the  above  circumstances. 
Rubber-covered  wires  or  cable  for  voltages  up  to  7  kv.  shall  be 
tested  in  accordance  with  the  National  Electric  Code.     Stand- 
ardization for  higher  voltages  for  rubber-insulated   cables  is 
not  considered  possible  at  the  present  time. 

Varnished-cambric  and  impregnated-paper  insulated  wires  or 


230     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


cables  shall  be  tested  at  the  place  of  manufacture  for  5  min. 
in  accordance  with  the  Table  XXX  below: 

TABLE  XXX. — RECOMMENDED  TEST  KILOVOLTS  CORRESPONDING  TO  OPER- 
ATING KILOVOLTS 


Operating  kv. 

Test  kv. 

Operating  kv. 

Test  kv. 

Below  0.5 

2.51 

5 

14 

0.5 

3.0 

10 

25 

1.0 

4.0 

15 

35 

2.0 

6.5 

20 

44 

,       3.0 

9.0 

25 

53 

4.0 

11.5 

1  The  minimum  thickness  of  insulation  shall  be  He  in-  (1-6  mm.). 

Different  engineers  specify  different  thickness  of  insulation 
for  the  same  working  voltages.  Therefore,  at  the  present  time 
the  test  kilovoltage  corresponding  to  working  kilovoltage  given 
in  Table  XXX  are  based  on  the  minimum  thickness  of  the  insula- 
tion specified  by  engineers  and  operating  companies.1 

685.  The  frequency  of  the  test  voltage  shall  not  exceed  100  cycles 
per  sec.,  and  should  approximate  as  closely  as  possible  to  a  sine 
wave.     The  source  of  energy  should  be  of  ample  capacity. 

686.  Where  ultimate  breakdown  tests  are  required,  these  shall  be 
made  on  samples  not  more  than  6  meters  (20  ft.)  long.     The 
maximum  allowable  temperature  at  which  the  test  is  made  for 
the  particular  type  of  insulation  and  the  particular  working 
pressure,  shall  not  be  greater  than  the  temperature  limits  given 
in  paragraph  677. 

687.  Multiple-conductor  Cables. — Each  conductor  of  a  multiple- 
conductor  cable  shall  be  tested  against  the  other  conductors 
connected  together  with  the  sheath  or  water. 

INSULATION  RESISTANCE. 

688.  Definition. — The   insulation  resistance   of   an   insulated 
conductor  is  the  electrical  resistance  offered  by  its  insulation, 
to  an  impressed  voltage,  tending  to  produce  a  leakage  of  current 
through  the  same. 

1  The  Standards  Committee  does  not  commit  itself  to  the  principle  of 
basing  test  voltages  on  working  voltages,  but  it  is  not  yet  in  possession  of 
sufficient  data  to  base  them  upon  the  dimensions  and  physical  properties 
of  the  insulation. 


TESTING  OF  CABLES  231 

689.  Insulation  resistance  shall  be  expressed  in  megohms  for 
a  specified  length  (as  for  a  kilometer  or  a  mile  or)  1,000  ft.,  and 
shall  be  corrected  to  a  temperature  of  15.5°C.,  using  a  tempera- 
ture coefficient   determined  experimentally  for  the  insulation 
under  consideration. 

690.  Linear  insulation  resistance,  or  the  insulation  resistance 
of  unit  length,  shall  be  expressed  in  terms  of  the  megohm-kilo- 
meter, or  the  megohm-mile,  or  the  megohm-1,000  ft. 

691.  Megohms    Constant. — The    Megohms    Constant    of    an 
insulated  conductor  shall  be  the  factor  (K  in  the  equation) 

R  =  K  logio  -£ 

where  R  =  the  insulation  resistance,  in  megohms,  for  a  specified 
unit  length. 

D  =  the  outside  diameter  of  insulation. 

d   =  the  diameter  of  conductor. 

Unless  otherwise  stated,  K  will  be  assumed  to  correspond  to 
the  mile  unit  of  length. 

692.  Test. — The  apparent  insulation  resistance  should  be  meas- 
ured after  the  dielectric  strength  test,  measuring  the  leakage 
current  after  a  1-min.  electrification,  with  a  continuous  e.m.f.  of 
from  100  to  500  volts,  the  conductor  being  maintained  positive 
to  the  sheath  of  water. 

693.  Multiple-conductor  Cables. — The  insulation  resistance  of 
each  conductor  of  a  multiple-conductor  cable  shall  be  the  insula- 
tion resistance  measured  from  such  conductor  to  all  the  other 
conductors  in  multiple  with  the  sheath  or  water. 

CAPACITANCE   OR  ELECTROSTATIC  CAPACITY. 

694.  Capacitance  is  ordinarily  expressed  in  microfarads.    Linear 
Capacitance  or  Capacitance  per  unit  length,  shall  be  expressed 
in  microfarads  per  unit  length  (kilometer,  or  mile,  or  1,000ft.). 
and  shall  be  corrected  to  a  temperature  of  15.5°C. 

695.  Microfarads  Constant. — The  Microfarads  Constant  of  an 
insulated  conductor  shall  be  the  factor  K  in  the  equation: 

c-     K 

D 

Log10  - 


232     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

where  C  =  the  capacitance  in  microfarads  per  unit  length. 
D  =  the  outside  diameter  of  insulation. 
d   =  the  diameter  of  conductor. 

Unless  otherwise  stated,  K  will  be  assumed  to  refer  to  the  mile 
unit  of  length. 

696.  Measurement  of  Capacitance. — The  capacitance  of  low- 
voltage  cable  shall  be  measured  by  comparison  with  a  standard 
condenser  for  long  units  of  high-voltage  cables,  where  it  is  neces- 
sary to  know  the  true  capacitance  the  measurement  should  be 
made  at  a  frequency  approximating  the  frequency  of  operation. 

697.  Paired  Cables. — The  capacitance  shall  be  measured  be- 
tween the  two  conductors  of  any  pair,  the  other  wires  being 
connected  to  the  sheath  or  ground. 

698.  Electric  Light  and  Power  Cable. — The  capacitance  of  low- 
voltage  cables  is  generally  of  but  little  importance.     The  capaci- 
tance of  high-voltage  cables  should  be  measured  between  the 
conductors  and   also   between  each   conductor  and   the  other 
conductors  connected  to  the  lead  sheath  or  ground. 

699.  Multiple-conductor   Cables    (Not   Paired). — The   capaci- 
tance of  each  conductor  of  a  multiple-conductor  cable  shall  be 
the  capacitance  measured  from  such  conductor  to  all  of  the 
other  conductors  in  multiple  with  the  sheath  or  the  ground. 

NOTE. — The  paragraph  numbers  refer  to  sections  in  the  Ameri- 
can Institute  of  Electrical  Engineers  Standardization  Rules. 

CAPACITY  OF  TESTING  APPARATUS. 

The  size  of  electrical  apparatus  necessary  in  voltage  testing, 
with  alternating  current  is  not  generally  appreciated.  This 
may  be  due  to  the  fact  that  as  these  tests  are  made  on  open  cir- 
cuits, many  persons  assume  no  current  is  required.  However, 
there  is  current  flowing  and  the  amount  is  shown  by  the  formula: 

2<irfCE 
1,000,000 
where 

I  =  current  flowing  into  the  cable. 

E  =  testing  voltage. 

/   =  frequency. 

C  =  electrostatic  capacity  of  cable  in  microfarads. 

But  .the  size  of  apparatus  is  dependent  upon  the  watts  required 
or 


TESTING  OF  CABLES  233 

Size  =  Watts  =  /  X  E 

'          " 


1,000,000  "  1,000,000 

This  means  that  the  watts  are  proportional  to  the  frequency 
capacity  and  the  square  of  the  voltage,  and  on  high-voltage  tests 
this  means  large  apparatus.  For  instance,  1,000  ft.  of  a  500,000- 
cm.  cable  with  %2~m-  wall  of  30  per  cent.  Para  has  a  capacity  of 
about  0.33  microfarads.  With  a  frequency  of  25  cycles,  this  for- 
mula shows  that  1.3  kw.  capacity  is  required  to  test  at  5,000  volts. 
If  this  cable  were  to  be  tested  at  30,000  volts,  apparatus  36  times 
as  large,  or  of  about  47  kw.,  would  be  required.  If  60  cycles 
instead  of  25  were  used,  a  30,000-volt  test  would  mean  that  the 
apparatus  would  have  to  have  a  capacity  of  about  113  kw. 

According  to  the  best  information  available,  there  appears  to 
be  no  appreciable  difference  in  severity  between  testing  at  25  or 
60  cycles  on  ordinary  factory  tests. 

Locating  and  Repairing  Cable  Failures.  —  Numerous  methods 
have  been  tried  for  locating  faults  in  underground  transmission 
cables,  some  companies  depending  upon  the  use  of  an  intermittent 
current  on  the  damaged  cable,  which  is  then  explored  by  means 
of  an  induction  coil  and  telephone  receiver,  while  other  companies 
make  use  of  the  Murray  loop  test.  Most  companies  avail  them- 
selves more  or  less  of  the  method  of  inspection  when  locating 
faults  by  sending  men  over  the  route  of  the  cable. 

As  stated  by  W.  A.  Durgin,  in  a  paper  presented  before  the 
National  Electric  Light  Association  in  1910,  fault  location  ir 
high-tension  power  cables  requires  quite  a  different  procedure 
from  that  usually  outlined  in  texts  upon  cable  testing,  due  to  the 
wide  difference  in  the  characteristics  of  construction  between 
power  and  intelligence  transmissions.  The  "cut-and-try" 
method  is  applicable  to  both,  but  if  a  quicker  and  less  expensive 
system  is  desired  testing  equipment  of  special  design  must  be 
provided. 

Most  of  the  larger  companies  have  provided  themselves  with 
a  testing  transformer  which  is  used  in  connection  with  a  motor- 
driven  generator  to  supply  current  of  varying  voltage  for  the 
purpose  of  breaking  down  a  faulty  cable  or  applying  a  high- 
tension  test.  For  the  purpose  of  expediting,  as  much  as  possible, 
the  work  of  locating  and  repairing  a  cable  fault,  specific  rules 


234     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

should  be  prepared  governing  the  procedure  of  station,  substa- 
tion and  underground  men  in  such  cases. 

In  the  Proceedings  of  the  National  Electric  Light  Association, 
Underground  Committee,  1911,  the  report  of  two  companies 
gives  the  various  methods  by  which  the  cable  breaks  are  located, 
and  the  percentage  of  breaks  which  are  discovered  by  each 
method  as  follows: 


Method 

Company  A,  per  cent. 

Company  B,  per  cent. 

Loop  test 

15  0 

46 

Examination.  .  . 

36  5 

8 

Cut-and-try  

17.5 

28 

Reported.. 

24  3 

11 

Exploring  coil 

1  3 

7 

Miscellaneous  

5  4 

Most  companies,  before  applying  the  loop  test,  attempt  to 
obtain  a  dead  ground  on  one  phase  of  the  cable  by  breaking  it 
down  with  a  special  transformer  or  generator.  Following  a 
cable  breakdown,  and  while  the  location  of  the  break  is  being 
determined  it  is  customary  to  assemble  a  gang  of  underground 
repair  men,  with  tools  and  proper  means  of  transportation  at  some 
convenient  location  where  they  may  be  hurried  to  the  place  of 
the  burnout  as  soon  as  this  is  determined. 

Loop  Test. — Where  one  conductor  of  a  multiple-conductor 
cable  is  grounded  and  another  conductor  is  clear,  the  following 
adaption  of  the  loop  test  can  be  used  to  advantage.  This 
method  also  applies  to  single-conductor  cable  where  another 
conductor  is  available  for  the  return.  The  two  conductors  must 
be  of  the  same  size  or  corrections  will  have  to  be  made  for  the 
difference  in  the  resistance  of  the  two  sizes. 

The  grounded  conductor  is  jointed  to  the  good  conductor  at 
the  end  opposite  that  at  which  the  test  is  to  be  made.  A  resist- 
ance wire  is  used,  made  up  in  the  form  of  a  straight  wire  bridge 
or  wound  on  a  threaded  drum.  The  wire  is  calibrated  through- 
out its  length.  Contact  C,  referring  to  Fig.  108,  is  arranged 
that  it  can  be  moved  along  the  resistance  wire  throughout  its 
entire  length.  A  battery  is  connected  between  the  contact  C, 
and  the  galvanometer  between  the  terminals  A  and  B.  In 
making  test,  C  is  set  preferably  at  the  middle  point  of  the  resist- 
ance to  start  with.  When  contact  is  made,  the  galvanometer 


TESTING  OF  CABLES 


235 


will  swing  to  either  one  side  or  the  other,  depending  on  the 
location  of  the  ground.  Contact  C  is  then  moved  along  the 
resistance  wire  until  no  deflection  is  obtained  upon  the  galva- 
nometer. It  will  be  evident  that  the  distance  from  A  to  C  of 


FIG.  108. — Loop  method  of  locating  grounds  on  underground  cables. 

the  resistance  wire  will  represent  the  distance  from  A  to  G  on 
the  conductor  which  is  grounded. 

This  can  be  represented  by  the  following  formula,  wherein 
L  represents  the  total  length  of  the  conductors  joined  together, 


FIG.  109.— Portable  fault  localizes 

and  AC  and  BC  represents  the  relative  distance  measured  on  the 
resistance  arm. 

AC     AG       AC         AG 


Solving, 


BC      BG]  or  BG  ~  L  -AG' 


AG  = 


AC  (L  -  AG) 
CB 


236     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

A  portable  fault  localizer  is  illustrated  in  Fig.  109. 

It  is  an  application  of  the  Wheatstone  bridge  with  all  the 
necessary  apparatus  contained  in  one  portable  case  wired  for 
connection  to  the  circuit  to  be  tested. 

Its  use  assumes  that  the  cable  is  grounded  at  only  one  point 
and  that  a  parallel  conductor  of  the  same  length  and  resistance 
as  the  faulty  cable  is  available. 

After  all  electrical  connections  to  the  defective  feeder  have  been 
removed  and  before  the  fault  localizer  has  been  connected  to  the 
cable,  the  cable  is  tested  by  means  of  a  temporary  connection 
through  a  lamp  bank  or  battery  for  the  grounded  conductor. 
If  the  lamps  do  not  burn  brightly,  a  high-resistance  ground  is 


l-=>>\ 


o 


,000 

>ooo 


FIG.  110. — Diagram  of  connections  for  cable  fault  localizer. 

indicated  and  should  be  broken  down  by  applying  a  sufficiently 
high  voltage. 

The  fault  localizer  is  connected  as  shown  in  the  diagram  (110) 
and  the  dial  revolved  by  means  of  the  knob  in  the  middle  of  the 
localizer  until  the  galvanometer  shows  no  deflection  when  the 
key  is  closed.  The  reading  of  the  instrument  then  shows  the 
per  cent,  of  length  of  the  feeder  from  the  point  where  the  test  is 
being  made  to  the  location  of  the  ground,  assuming  the  total 
length  of  the  feeder  to  be  100  per  cent. ;  the  red  scale  indicating 
that  the  ground  is  on  the  conductor  connected  to  the  binding  post 
marked  red,  and  the  black  scale  indicating  that  it  is  on  the 
conductor  connected  to  the  binding  post  marked  black. 

Only  direct  current  is  used  in  these  tests. 

In  this  instrument  all  necessary  apparatus  is  contained  in 
one  case  and  it  has  the  further  advantage  of  easy  adjustment. 
The  position  of  the  ground  may  be  read  directly  on  the  dial  in 
terms  of  per  cent,  of  length  of  cable. 


TESTING  OF  CABLES  237 

Fault-locating  Equipment. — In  any  central-station  system  the 
most  important  work  in  connection  with  trouble  finding  is  the 
quick  and  accurate  location  of  a  break  in  a  three-phase  trans- 
mission cable.  With  the  advent  of  high-tension  cables  came  a 
problem  which  hitherto  had  not  obtained  to  any  great  extent, 
namely,  the  difficulty  of  obtaining  a  closed  circuit  for  testing 
current  across  the  break,  as  on  this  closing  of  the  signaling  cir- 
cuit through  the  fault  hinges  the  success  of  all  methods  employ- 
ing interrupted  or  varying  current,  with  the  exploring  coil  and 
telephone  receiver.  Almost  invariably  in  high-tension  cable 
breaks,  there  is  no  metallic  path  between  conductors,  or  between 
conductor  and  sheath;  a  thick  wad  of  paper  or  other  insulation 
intervening,  through  which  a  path  must  be  carbonized  to  com- 
plete the  testing  circuit.  With  the  application  of  sufficient  pres- 
sure and  current  this  path  through  the  insulating  medium  can 
be  made  and  maintained,  while  the  fault  is  being  located  with 
the  exception  of  cases  where  the  break  is  submerged  in  water, 
or  where  the  cable  is  burned  completely  open. 

There  is  a  wide  variation  in  the  resistance  in  faults  in  high- 
tension  cables;  a  cable  may  break  down  with  a  working  pressure 
of  13,000  volts,  and  upon  applying  a  100-volt  test  show  practi- 
cally a  short-circuit  through  the  fault.  The  next  breakdown  in 
the  same  cable  may  take  5,000  volts  to  even  indicate  the  existence 
of  trouble.  It  is,  therefore,  obvious  that  it  is  necessary  to  have 
a  test  set  of  sufficient  pressure  to  obtain  a  flow  of  current  across 
the  break.  It  is  also  desirable  to  be  able  to  vary  this  pressure 
as  in  the  use  of  signaling  currents;  the  best  results  are  obtained 
with  the  testing  voltage  as  low  as  possible.  Again,  on  account 
of  the  electrostatic  capacity  of  long  cables,  a  certain  amount  of 
current-carrying  capacity  in  the  apparatus  is  required.  While 
it  is  unnecessary  that  this  be  as  large  as  is  required  for  a  break- 
down test  on  a  sound  cable,  yet  it  should  be  of  a  considerable 
value  depending  upon  the  length  and  working  voltage  of  the  line 
in  trouble. 

There  are  some  cable  faults  through  which  it  is  necessary  to 
maintain  a  steady  flow  of  current  at  a  certain  pressure  in  order 
to  hold  the  conducting  path  across  the  break.  This  current 
should  be  of  a  small  value  so  as  to  obviate  the  danger  of  damaging 
the  adjacent  cable  and  also  to  reduce  the  prospect  of  destroying 
the  conducting  path  by  combustion.  These  conditions  are  met 
by  the  use  of  the  method  and  apparatus  herein  described  which 


238     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

has  been  used  for  a  number  of  years  in  a  large  central-station 
system.  With  this  device  it  is  possible  to  locate  quickly  and 
accurately  grounds,  short-circuits,  crosses  and  opens  in  under- 
ground and  overhead  lines,  whether  the  lines  are  carrying  work- 
ing current  or  not,  also  to  identify  for  tagging  different  wires 
and  cables  alive  or  dead,  and  to  pick  out  the  phase  wires  of  an 
alternating  circuit  on  the  poles,  in  the  manholes,  or  on  the 
customer's  premises,  without  any  interruption  or  interference 
whatever  in  the  operation  of  the  system. 

The  test  set  comprises  two  parts,  the  apparatus  for  the  reduc- 
tion of  the  fault  resistance  and  carbonizing  of  the  path  across 
the  insulation  medium,  and  the  signaling  device  with  exploring 
coils  and  telephone  receivers. 

For  the  location  of  faults  in  No.  %  paper^insulated  cables 
of  5  miles  and  under,  the  capacity  of  the  set  is  7.5  kw.  and  for 
over  5  miles  in  length,  15  kw.  In  general,  the  maximum  pres- 
sure of  the  apparatus  should  be  one-half  the  greatest  working 
pressure  of  the  underground  system,  and  in  the  set  in  question 
the  pressures  obtainable  are  115-230-575-1,150-2,300-3,450- 
4,600-5,750-6,900  volts.  These  voltages  are  derived  from 
standard  lighting  transformers  connected  in  different  combina- 
tions to  obtain  varying  pressures.  The  signaling  part  of  the 
apparatus  consists  of  a  very  powerful  sound-producing  device 
which  takes  current  directly  from  either  alternating  current  or 
direct  current  mains.  A  specially  designed  motor-driven  inter- 
rupter produces  a  signal  current  of  a  frequency  to  which  the  tele- 
phone receiver  and  the  human  ear  are  most  responsive  and  which, 
though  extremely  small  in  value,  produces  signals  which  are 
easily  heard.  The  voltage,  current,  and  tone  of  the  signaling 
circuit  can  be  varied  at  will.  It  will  interrupt  either  alternating 
current  or  direct  current  giving  a  distinctly  different  tone  on 
each.  Wherever  alternating  current  is  available  it  is  used  in 
preference  to  direct  current  as  the  apparatus  is  somewhat  simpler. 

This  interrupter  is  of  rugged  construction,  can  be  used  on  the 
system  voltage,  in  conjunction  with  the  ordinary  transformer, 
and  will  run  for  hours  without  any  attention  whatever,  giving 
out  a  never- varying  signal. 

While  this  outfit  is  designed  to  be  set  up  permanently  in  the 
station,  a  portable  set  of  about  3  kw.  capacity  can  be  used  where 
necessary.  This  is  capable  of  handling  practically  all  faults 
except  those  submerged  in  water  or  of  very  high  resistance. 


TESTING  OF  CABLES  239 

The  apparatus  is  designed  to  be  used  by  the  ordinary  trouble 
hunter  without  the.  use  of  laboratory  instruments,  and  it  can  be 
used  to  advantage  in  conjunction  with  the  power  bridge  loop 
and  capacity  instruments,  etc.,  to  locate  faults  exactly  without 
opening  any  joints  in  cables. 

The  signaling  system  can  be  adapted  to  any  existing  type  of 
breakdown  apparatus. 

It  is  often  desirable  to  be  able  to  pick  out  the  different  legs  or 
phases  of  an  alternating  circuit,  at  some  point  distant  from  the 
source  of  supply.  This  can  be  done  by  superposing  the  inter- 
rupted currents  on  the  primary  line  through  an  ordinary  trans- 
former without  any  interference  in  the  working  of  the  circuit. 
By  applying  the  exploring  coils  to  the  different  wires  of  the  cir- 
cuit it  can  be  determined  to  which  pair  the  interrupter  is  con- 
nected. Likewise,  if  it  is  desired  to  know  which  phase  supplies 
a  certain  customer,  by  attaching  a  plug  to  a  lamp  socket  and 
listening  through  a  telephone  receiver  connected  to  a  special 
type  of  coil,  this  can  be  readily  determined. 

A  diagnosis  and  a  somewhat  predictive  location  of  faults  can 
be  made  with  a  little  experience  in  working  the  apparatus. 
Faults  in  water  show  certain  characteristics  and  the  wet  holes 
being  known,  some  idea  is  given  of  the  location  of  the  breaks. 
Experience  in  carbonizing  a  fault  shows  whether  it  is  in  a  section 
of  cable  or  in  a  joint  by  measuring  the  charging  current  the 
distance  to  an  open  end  can  be  approximately  figured.  If  there 
is  a  cross  between  the  live  side  of  a  grounded  secondary  and  a 
primary  or  street-lighting  circuit,  this  can  be  shown  in  advance. 
Advantage  can  be  taken  of  the  phenomenon  of  resonance  to 
discriminate  between  the  natural  leakage  and  charging  current 
of  a  circuit,  and  fault  current,  all  of  which  makes  it  much  easier 
to  locate  trouble. 

For  secondary  networks,  and  breaks  in  low  resistance,  on 
isolated  lines  and  cables,  a  portable  vibrating  interrupter,  which 
will  operate  on  two  dry  cells,  has  been  developed.  This  inter- 
rupter gives  a  very  good  signal  and  can  be  heard  through  1,000 
ohms  resistance.  While  the  foregoing  apparatus  is  intended 
primarily  for  underground  cables  it  can  be  used  with  the  same 
success  on  overhead  lines. 

The  method  and  apparatus  was  devised  by  James  A.  Vahey,  of 
the  Edison  Electric  Illuminating  Co,  of  Boston,  Mass, 


240     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

Periodic  High-potential  Testing  of  Transmission  Cables.— 
There  is  a  great  variation  of  opinion  in  regard  to  the  advisability 
of  periodically  testing  transmission  cables.  It  is  the  practice  of 
most  companies  to  apply  a  breakdown  test  of  150  to  200  per 
cent,  of  working  voltage  on  new  lines  for  an  average  time  of  5 
min.  In  some  cases  cables  are  subjected  to  high-potential  test 
only  after  meager  tests  show  a  low  value  or  after  a  series  of 
breakdowns. 

The  following  regarding  high-potential  testing  is  taken  from 
the  National  Electric  Light  Association,  Underground  Committee 
report. 

Some  companies  subject  their  cables  to  a  high-potential  test, 
once,  twice  and  even  three  times  a  year,  with  pressures  as  high 
as  three  times  normal  working  voltage.  Other  companies  make 
insulation  tests  only,  unless  the  record  of  any  cable  should  show  a 
gradual  decrease  in  insulation  resistance,  in  which  case  it  would  be 
subjected  to  a  high-potential  test  to  break  down  the  developing 
defect.  Several  cases  of  incipient  trouble  have  been  discovered 
and  eliminated  by  this  method,  but  it  has  not  always  proved 
successful. 

One  large  company  started  to  make  high-potential  tests  on  all 
of  its  cables  twice  a  year,  but  for  various  reasons  this  practice 
was  soon  abandoned.  With  the  numerous  changes  in  its  under- 
ground system  and  the  practice  of  subjecting  cables  to  a  high- 
potential  test  after  any  changes  have  been  made  on  them,  many 
of  the  lines  thus  obtained  a  test  indirectly.  A  few  cases  occurred 
in  which  lines  withstood  the  test  but  broke  down  shortly  after- 
ward, notably  one  case  in  which  the  lead  sheath  of  the  cable 
was  damaged  by  electrolysis.  This  cable  burned  out  a  few  days 
after  the  high-potential  test,  and  an  examination  of  the  cable 
showed  that  there  must  have  been  a  hole  in  the  lead  sheath  for 
several  weeks  previous  to  the  test. 

Several  companies  are  now  installing  apparatus  with  the  view 
of  making  periodic  high-potential  breakdown  tests  on  all  of  their 
transmission  lines,  while  other  companies  which  already  have  the 
necessary  equipment  have  abandoned  the  practice  of  making  such 
test. 

In  general,  it  might  be  said  that  high-potential  tests  increase 
the  liability  to  subsequent  breakdowns  and  often  do  not  disclose 
existing  points  of  weakness. 


CHAPTER  VIII 
DISTRIBUTION  SYSTEMS  AND  AUXILIARY  EQUIPMENT 

General. — In  dealing  with  systems  of  distribution,  no  attempt 
will  be  made  to  take  up  the  solution  of  all  of  the  electrical  prob- 
lems involved,  numerous  text-books  and  reports  of  engineering 
associations  having  covered  this  subject  in  considerable  detail. 
Modern  three-wire  direct-current  distributing  systems  consist 
essentially  of  a  three-wire  network  of  distributing  mains  with 
numerous  cable  feeders  delivering  current  at  different  points 
in  the  network,  the  current  being  supplied  by  a  system  of  sub- 
stations. Since  the  direct-current  system  of  underground  dis- 
tribution is  confined  so  largely  to  the  Edison  system,  which 
has  been  developed  to  a  high  degree  of  perfection  and  in  which 
most  of  the  problems  in  handling  low-potential  current  have 
been  solved,  it  is  thought  unnecessary  to  include  this  subject  in 
the  discussion. 

Alternating-current  Distribution. — The  secondary  network  in 
an  alternating-current  system  is  practically  identical  in  its  es- 
sential details  with  its  predecessor,  the  direct-current  network, 
and,  therefore,  had  a  number  of  its  problems  already  solved. 
However,  the  higher  voltages  employed  in  the  alternating-current 
system  brought  about  difficulties  which  have  been  satisfactorily 
overcome  only  after  years  of  experience  and  effort. 

The  distribution  of  alternating  current  for  general  commercial 
purposes  is  accomplished  in  America  almost  universally  by  2,200- 
volt  mains  supplying  step-down  transformers  located  near  groups 
of  consumers  who  are  served  by  secondary  mains  at  110  to  220 
volts.  Lighting  service  is  quite  generally  single-phase;  while 
power  service  is  more  frequently  two-phase  or  three-phase. 
Two-phase  systems  are  in  use  chiefly  where  this  method  of  dis- 
tribution was  established  in  the  early  period  of  development  and 
is  too  extensive  to  warrant  changing  to  the  three-phase  system. 
Three-phase  systems  are  now  standard  for  nearly  all  new  power 
installations.  Alternating-current  underground  distribution  in 
general  conforms  to  established  overhead  practice  so  far  as  voltage, 
16  241 


242     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

character  of  service  and  regulation  are  concerned.  Alternating- 
current  systems  are  divided  into  primary  and  secondary  dis- 
tribution, which  may  be  subdivided  into  single-phase,  two-phase 
(three-  and  four- wire),  and  three-phase  (three-  and  four- wire) 
systems. 

Single-phase. — In  the  early  days  of  the  industry  all  distribu- 
tion was  single-phase.  This  system  is  very  simple  to  install  and 
maintain  but  has  the  serious  disadvantage  of  not  being  well 
adapted  for  power  loads  except  where  the  motors  are  of  small 
rating.  Single-phase  motors  are  not,  as  a  rule,  manufactured  in 
large  sizes  because  their  design  is  complicated  and  expensive  and, 


FIG.  111. — Single-phase  two  and  three-wire  system.     The  fuses  on  the 
secondary  side  of  the  transformer  may  be  omitted. 

since  they  are  not  self-starting,  a  costly  split-phase  starting  con- 
trol is  a  necessary  part  of  the  motor  equipment. 

As  a  rule,  straight  single-phase  primary  distribution  is  not 
employed  except  in  scattered  districts  where  the  diversity  factor 
is  such  as  to  make  the  loading  of  a  single-phase  circuit  more 
economical  than  that  of  a  polyphase  circuit. 

A  single-phase,  two- ,  and  three-wire  system  is  illustrated  in 
Fig.  111. 

Two-phase. — A  two-phase  system  is  supplied  by  a  generator 
which  generates  two  voltages  which  are  in  quadrature,  i.e.,  one 
voltage  is  a  quarter  cycle  behind  the  other.  This  system  pos- 
sesses the  same  advantages  as  the  single-phase  system  as  regards 
economical  loading  of  circuits  butjias,  in  addition,  the  important 


DISTRIBUTION  SYSTEMS 


243 


advantage  that  it  may  be  used  to  take  care  of  motor  loads 
without  the  use  of  the  expensive  starting  apparatus  required 
by  a  single-phase  motor. 


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FIG.  112. — Two-phase,  three-wire  system. 


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FIG.  113. — Two-phase,  four-wire  system. 

The  two-phase  system  may    be    either  three  or  four-wire. 
Where  used  as  a  four-wire  system,  the  transmission  of  energy 


244     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

is  in  effect  single-phase.  The  distribution  of  energy,  however, 
is  a  combination  of  single-  and  two-phase,  since  the  lighting  load 
is  taken  care  of  on  a  number  of  single-phase  taps  made  in  such  a 
way  that  the  load  is  balanced  between  A  and  B  phases,  while 
the  motor  load  makes  use  of  both  phases. 

In  the  two-phase,  three-wire  system,  two  of  the  four  wires 
are  replaced  by  a  single  wire  called  the  neutral,  the  cross-section 
of  which  is  theoretically  41.4  per  cent,  greater  than  either  of  the 
other  two.  The  three-wire  system  requires  less  copper  than  the 


V  CONNECT/ON 


FIG.  114.  —  Three-phase,  three-wire  system. 


four-wire  for  the  same  current-carrying  capacity  but  it  is  less 
flexible,  and  good  regulation  is  difficult  because  load  conditions 
on  one  phase  will  affect  the  other  phase,  thereby  producing  un- 
balanced voltages. 

Two-phase,  three-wire,  and  two-phase,  four-wire  systems  are 
shown  in  Fig.  112  and  113. 

Three-Phase.  —  The  three-phase  system  may  be  used  with 
either  three  or  four  wires.  The  three-wire  system  may  be  either 
A-  or  7-connected;  and  where  good  load  balances  may  be  obtained, 
it  is  very  satisfactory.  However,  a  balanced  load  is  difficult  to 
obtain;  and  where  the  load  is  unbalanced,  there  is  a  shifting 
of  the  neutral,  with  the  result  that  voltage  regulation  is 


DISTRIBUTION  SYSTEMS 


245 


difficult.  For  this  reason  the  four-wire  system  has  many 
advantages  over  the  three-wire  system  and  has  been  adopted 
in  many  of  the  best  installations.  In  this  system,  which  is 
7-connected,  a  neutral  wire  carries  the  unbalanced  current, 
making  it  possible  to  obtain  good  voltage  regulation  on  all  three 
phases  even  when  a  condition  of  considerable  unbalance  exists. 
Since  this  neutral  wire  is  at  approximately  ground  potential;  it 
will  be  seen  that  it  is  possible  to  transmit  at  considerably  higher 
voltage  between  phases  without  increasing  the  potential  of  the 
system  with  respect  to  ground.  For  instance,  a  three-phase, 


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FIG.  115.  —  Three-phase,  four-wire  system. 

three-wire  system  with  2,400  volts  between  phases  may  be  re- 
placed by  a  three-phase,  four-wire  system  with  approximately 
4,100  volts  between  phases  without  raising  the  voltage  to  ground. 
This  results  in  a  reduction  in  the  size  of  the  conductors,  which 
is  only  partly  offset  by  the  increased  cost  of  the  neutral  wire. 

Three-phase,  three-wire,  and  three-phase,  four-wire  systems 
are  shown  in  Figs.  114  and  115. 

The  following  table  gives  a  comparison  of  the  weights  of  wire 
required  by  the  various  systems  based  on  the  single-phase  system 
as  100  per  cent,  transmitted  load  and  other  conditions  being 
equal. 


246     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

TABLE  XXXI 


System 

Size  of  wire 

Per  cent,  of 
single-phase, 
two-  wire 

Single-phase,  two-wire  

100.00 

Two-phase,  three-wire 

Neutral  equal  to  outside 

75  00 

Two-phase,  three-wire  
Two-phase,  four-wire  

Neutral  1.41  times  outside..  .  . 

72.90 
100.00 

Three-phase  three-wire 

75  00 

Three-phase  four-wire  . 

Neutral  equal  to  outside 

33  30 

Three-phase,  four-wire  . 

Neutral  one-half  outside. 

29  16 

Secondary  Mains. — The  arrangement  of  secondary  mains 
depends  largely  upon  the  density  of  the  load.  In  outlying  dis- 
tricts where  the  load  runs  from  1  to  10  kw.  in  each  block,  the 


FIG.  116. — A.  C.  primary  and  secondary  distribution  system,  showing  use  of 
junction  boxes  and  fuses. 

size  of  secondary  wires  is  comparatively  small  and  the  distance 
between  transformers  is  such  that  the  interconnection  of  adjacent 
secondary  mains  is  not  commonly  considered  desirable.  In 
the  denser  parts  of  a  city,  where  business  buildings  are  served, 
a  cross-connected  network  is  frequently  developed.  The  inter- 
connection of  secondary  mains  has  the  advantages  of  making 
use  of  spare  capacity,  by  equalizing  loads  on  adjacent  trans- 
formers. The  network  is  the  last  step  in  the  development  of  a 
system  of  secondary  mains,  the  gradual  extension  of  mains  on  all 


DISTRIBUTION  SYSTEMS 


247 


intersecting  streets  resulting  in  a  system  of  lines  which  is  inter- 
connected thus  forming  a  network.  In  the  design  of  networks, 
the  selection  of  sizes  of  secondary  cable  is  restricted  by  the  practi- 
cal conditions  in  each  locality.  The  smaller  and  more  widely  dis- 
tributed consumers  are  carried  on  mains  of  proper  size  to  deliver 
the  total  energy  demanded.  Large  consumers,  such  as  theatres 
and  department  stores  are  usually  more  economically  cared  for 
by  a  separate  installation  of  transformers  in  the  immediate 
vicinity  of  the  consumer's  premises. 

The   desirability   of   establishing   centers   of   distribution  to 
which  a  circuit  is  run  directly  from  the  substation  without  other 


VNV™™*V™VYW 


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FIG.  1 17. — A.  C.  distribution  system,  showing  use  of  oil  switches. 

connections  has  led  to  the  development  of  several  schemes  for 
interconnecting  or  disconnecting  circuits  at  central  distributing 
points,  as  may  be  required  in  the  operation  of  the  system. 
Among  these  methods  attention  is  called  to  the  use  of  junction 
boxes  equipped  with  fuses  or  solid  connectors,  adapted  for  easy 
removal  or  manipulation  in  order  to  accomplish  the  desired  result. 
Another  scheme  includes  the  use  of  manual  non-automatic  oil 
switches  connected  in  distributing  circuits  for  sectionalizing  and 
disconnecting  purposes.  In  a  few  instances  recourse  has  been  had 
to  automatic  switches,  or  special  forms  of  high-tension  fuses  of 
either  the  oil  or  cartridge  type,  arranged  to  automatically  discon- 
nect faulty  sections  of  primary  circuits  from  the  main  circuit. 


248     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

Typical  arrangements  of  these  schemes  are  outlined  in  Figs, 
lift  and  117,  which  show  the  method  of  applying  the  various 
devices  referred  to  for  sectionalizing  and  interconnecting  pur- 
poses, as  well  as  for  disconnecting  circuits  to  improve  working 
conditions. 

Underground  Transformers. — The  method  of  installing  trans- 
formers, standard  subway  types  of  which  are  on  the  market, 
plays  a  very  important  part  in  the  successful  operation  of  an 
alternating-current  underground  distribution  system.  Trans- 
formers as  now  manufactured,  when  properly  installed  and  cared 
for,  will  give  reasonably  reliable  service  without  automatic  pro- 
tection. The  practice,  however,  varies  with  different  companies, 
some  using  fuses  or  automatic  protection  in  connection  with 
every  manhole  transformer,  and  others  connecting  them  solid. 
Transformers  for  underground  installation  must  possess  certain 
features  in  order  successfully  to  meet  all  service  conditions.  The 
following  may  be  mentioned  as  especially  important. 

They  must  be  water-tight,  as  subways  are  not  always  dry. 
They  must  be  properly  proportioned  for  the  limited  space 
available  in  manholes,  and  they  must  have  small  iron  losses 
because  they  are  continuously  connected  to  the  mains.  The 
radiating  surface  must  be  large  and  the  temperature  rise  small, 
since  the  manholes  are  practically  air-tight,  limiting  the  dissi- 
pation of  heat.  While  in  the  past  manufacturers  have  considered 
that  underground  transformers  should  be  provided  with 
emergency  relief  valves  or  vents  in  order  to  prevent  the  creation 
of  dangerous  pressures  within  the  transformer  cases,  it  may 
be  definitely  stated  that  the  use  of  such  devices  is  entirely  unneces- 
sary and  their  omission  is  recommended  in  all  cases.  An  exhaus- 
tive study  of  underground  transformer  troubles  by  the  National 
Electric  Light  Association  Committee  on  Underground  Construc- 
tion reveals  the  fact  that  many  troubles  may  be  traced  directly 
or  indirectly  to  the  use  of  relief  devices  or  to  poor  electrical  con- 
nections resulting  from  careless  or  improper  installation  methods. 
Troubles  caused  by  the  occasional  flooding  of  transformer 
manholes  where  relief  devices  have  been  in  use  may  be  emphasized 
as  a  reason  for  their  omission,  as  many  cases  of  transformer 
failures  are  directly  traceable  either  to  water  or  moisture  enter- 
ing the  relief  device  or  the  transformer  case  through  loose  covers 
or  other  points  of  entrance  which  have  not  been  properly  sealed 
at  the  time  of  installation. 


DISTRIBUTION  SYSTEMS  249 

The  importance  of  maintaining  the  oil  in  underground  trans- 
formers in  perfect  condition,  free  from  moisture  or  sediment, 
cannot  be  too  strongly  emphasized,  as  the  life  of  the  transformer 
depends  on  the  elimination  of  these  conditions. 

Precautions  should  be  taken  by  operating  companies  to  insure 
proper  installation  and  operation  of  transformers,  and  in  addi- 
tion to  an  inspection  of  the  oil  at  least  once  a  year,  air  pressure 
should  be  applied  to  the  transformer  cases  after  installation  to 
detect  leaks.  Transformers  should  be  so  placed  in  the  under- 
ground chamber  that  the  oil  gage  and  oil  drain  are  readily  visible 
and  accessible. 

The  transformer  should  be  subjected  to  an  air  pressure  of 
about  6  Ib.  per  sq.  in.  when  full  of  oil  and  after  the  line  and  feeder 
connections  have  been  made.  To  make  the  air-pressure  test, 
any  convenient  device,  such  as  a  small  air  pump  used  to  inflate 
automobile  tires,  can  be  used  to  establish  the  required  pressure. 

The  chief  transformer  difficulties  which  most  companies 
encounter  are  caused  by  the  flooding  of  subways  and  manholes. 
Occasional  failures  in  the  cable  connections  to  the  transformers 
have  also  contributed  to  the  list  of  troubles  in  this  class  of  service. 
If  water  gets  into  the  transformer  tank,  it  will  be  necessary  to 
dry  out  the  transformer  before  it  is  again  placed  in  service. 
The  simplest  method  of  doing  this  is  as  follows:  Drain  off  all 
the  oil  from  the  transformer.  Then,  with  the  cover  off,  circulate 
sufficient  current  through  the  coils  to  maintain  a  temperature  of 
about  80°C.  With  the  secondary  coils  short-circuited,  about 
1^2  to  3  per  cent,  of  the  rated  voltage  applied  to  the  primary 
windings  should  be  sufficient  to  produce  the  required  heating. 
The  temperature  may  be  determined  by  a  thermometer  between 
the  coils  and  in  good  contact  with  them.  During  the  first  hour 
of  this  operation  the  temperature  should  be  carefully  observed 
so  that  the  coils  will  not  attain  a  temperature  exceeding  the 
above-mentioned  value.  Under  ordinary  circumstances  10 
or  12  hr.  should  be  a  sufficient  length  of  time  to  properly  drive 
out  all  moisture  from  the  coils.  If,  however,  there  are  evidences 
of  moisture  at  the  end  of  this  time,  the  heating  should  be 
continued  several  hours  longer. 

Transformers  should  be  provided  with  cutout  subway  boxes 
on  both  primary  and  secondary  sides  if  they  feed  an  underground 
distribution  network.  If  they  feed  only  isolated  sections,  the 
cutout  on  the  secondary  side  may  be  omitted.  These  boxes  need 


250     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

not  necessarily  be  fused,  as  a  number  of  companies  consider  that 
fuses  give  more  or  less  trouble.  Several  companies  recommend 
the  omission  of  fuses  on  both  the  primary  and  secondary  sides, 
and  depend  for  protection  entirely  upon  the  automatic  devices 
in  the  station.  Fuses,  where  used,  are  between  150  and  200  per 
cent,  of  cable  capacity.  The  neutral  is  connected  solid  in  all 
cases,  and  is  usually  not  brought  into  the  junction  box.  The 
secondary  neutral  of  the  transformer  should  be  a  solid  copper 
conductor  where  it  enters  the  transformer  case.  If  stranded 
wire  is  used,  water  is  apt  to  be  siphoned  into  the  transformer  when 
manholes  are  flooded,  and  special  precaution  should,  therefore, 
be  taken  to  see  that  this  connection  is  made  water-tight. 

The  location  of  transformers  at  street  intersections  is  especially 
desirable  as  it  permits  of  the  supply  of  electricity  in  four  direc- 
tions from  one  unit.  With  alley  lines,  where  the  high-tension 
distribution  is  overhead,  it  is  sometimes  preferable  to  locate 
the  transformers  for  the  underground  secondaries  on  poles.  In 
large  installations,  transformers  are  usually  located  in  separate 
manholes  or  in  vaults  on  the  customer's  premises. 

It  is  usual  in  subway  systems  to  connect  transformers  in 
multiple  so  that  in  case  of  a  transformer  failure  the  service  may 
not  be  interrupted,  although  there  may  be  a  temporary  drop  in 
voltage  until  part  of  the  load  can  be  transferred  to  an  adjacent 
transformer  bank. 

Some  trouble  has  been  experienced  due  to  transformers  not 
operating  satisfactorily  in  parallel  and  it  has  been  necessary  in 
some  instances  to  install  reactors  in  the  transformer  cases  so  that 
the  load  may  be  properly  shared  by  the  different  units.  The 
operation  of  subway  transformers  in  multiple,  however,  has 
proved  a  valuable  means  of  safeguarding  service,  and  many 
failures  of  transformers  or  transformer  bushings  have  resulted  in 
no  interruption  of  service,  the  only  indication  of  trouble  being  a 
slight  lowering  of  voltage  at  the  immediate  load  supplied  by  the 
defective  transformer. 

No  particular  precaution  seems  to  be  necessary  to  conduct  heat 
away  from  transformer  manholes  except  with  large  installations, 
where  a  cold-air  intake  is  provided  at  the  bottom  of  the  manhole 
and  a  vent  at  the  top,  as  illustrated  in  Fig.  118.  These  are 
usually  placed  alongside  of  an  adjoining  building  where  such  ar- 
rangements can  be  made. 

In  temperate  zones,  transformers  of  moderate  capacities  may 


DISTRIBUTION  SYSTEMS 


251 


be  safely  installed  in  manholes  where  3  cu.  ft.  of  space  per  kva. 
is  provided,  without  installing  any  special  means  of  ventilation 
other  than  that  afforded  by  a  perforated  manhole  cover.  When 
the  concentration  of  transformer  capacity  in  a  single  manhole 
reaches  200  kva.  or  more,  under  conditions  where  the  space 


No.l          Ventilated  Cover 


Ventilated 
Cover 


FIG.  118. — Methods  of  ventilating  transformer  manholes. 

factor  must  be  reduced  below  the  limit  given  above,  some  special 
facilities  for  ventilation  must  be  provided  to  avoid  temperature 
rises  in  excess  of  those  allowed  and  guaranteed  as  permissible  by 
manufacturers.  Natural  ventilation  is  to  be  preferred  in  all 


252     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

cases  where  conditions  are  favorable  for  the  installation  of  suitable 
means  for  promoting  a  rapid  circulation  of  air  through  the  man- 
hole. In  some  cases  recourse  may  be  had  to  artificial  circulation 
by  placing  small  blowers  in  manholes  to  draw  air  in  or  out,  as 
may  be  convenient. 

In  general,  it  may  be  said  that  8  watts  of  transformer  losses 
may  be  allowed  per  sq.  ft.  of  wall  surface.  In  moist  soil  with 
ventilated  chamber,  12  watts  may  be  allowed;  while  under 
unfavorable  conditions  not  more  than  6  watts  per  sq.  ft.  would  be 
permissible.  The  total  surface,  including  roof  and  floor,  should 
be  included  when  determining  wall  surface. 

It  is  recommended  that  transformers  be  installed  directly  in 
contact  with  the  bottom  of  manholes,  and  not  blocked  up  off  the 
bottom  in  any  case  unless  the  transformer  case  is  reliably 
grounded. 

Some  of  the  most  serious  accidents  on  record  have  been  either 
indirectly  or  directly  the  results  of  shocks  received  from  trans- 
former cases  placed  on  wooden  blocks  in  manholes,  all  of  these 
accidents  being  primarily  due  to  a  failure  of  the  transformer  or 
wiring  connections,  whereby  high  potential  was  impressed  upon 
the  ungrounded  transformer  case. 

Cable  Junction  Boxes. — Due  to  the  wide  extent  of  territory 
covered  by  alternating-current  feeders  and  mains,  and  to  the  large 
load  connected  to  same,  suitable  emergency  ties,  junction  boxes, 
oil  fuses,  etc.,  must  be  provided  to  sectionalize  the  portions  of 
the  system  which  may  be  affected  or  upon  which  work  must  be 
performed.  The  necessity  of  these  auxiliary  devices  is  apparent 
when  one  considers  the  high  potential  of  the  alternating-current 
system  as  compared  with  the  low  potential  of  the  direct-current 
system. 

Undoubtedly  the  greatest  difficulty  has  been  in  the  develop- 
ment of  primary  fuses  and  junction  boxes.  If  one  is  to  judge  by 
the  widely  differing  types  of  these  devices  in  use,  engineers  are 
not  agreed  as  to  the  best  solution  of  this  problem.  Underground 
alternating-current  distribution  would  probably  now  be  more 
extensively  used  but  for  lack  of  confidence  in  the  primary  fuse  and 
means  for  quickly  and  safely  cutting  in  and  out  portions  of  a, 
primary  network  in  case  of  trouble. 

Low- voltage  cable  junction  boxes  for  250-  and  500-volt  opera- 
tion have  been  in  general  use  for  a  number  of  years,  but  the 
development  of  the  alternating-current  underground  system  of 


DISTRIBUTION  SYSTEMS 


253 


distribution  has  brought  about  a  demand  for  similar  subway 
boxes  for  use  at  higher  voltages.  Primary  fuse  boxes  in  which 
the  fuses  were  immersed  in  oil  have  been  used  by  some  companies, 
but  in  a  number  of  cases  their  operation  has  been  very  unsatis- 
factory. One  general  defect  of  a  number  of  oil  fuse  boxes  which 
have  been  on  the  market  in  the  past  is  that  little  or  no  effort  had 
been  made  to  dampen  the  effect  of  the  explosion  when  the  fuse 
was  blown,  the  explosion  of  the  fuse  often  bursting  the  box  casting 
itself,  and  also  at  times  throwing  the  oil  over  the  workmen. 
Boxes  of  recent  design,  however,  have  been  constructed  to 


FIG.  119. — Subway  box  with  fuse  immersed  in  oil. 

operate  successfully  by  the  use  of  a  special  form  of  fuse  holder, 
which  has  been  able  to  withstand  satisfactorily  the  explosion 
and  arc  of  a  blowing  fuse  without  damage  to  the  box  and  without 
disturbing  the  oil  contained  therein  to  any  noticeable  extent. 
This  form  of  box,  which  is  shown  in  Fig.  119,  is  not  provided  with 
a  relief  valve,  but  the  fuse  holder  consists  of  a  special  form  of 
cartridge  holder  with  an  insulating  handle  which  carries  the  wire 
fuse  through  the  center  and  connects  the  ends  to  the  fuse  clip  by 
ordinary  knife  blades.  The  fuse  wire  itself  is  so  built  that  the 
overload  current  blows  it  at  the  center,  and  the  result  of  the 
explosion  is  greatly  dampened  by  means  of  a  cushion  of  air 
trapped  in  the  upper  part  of  the  horizontal  tube  mounted  in  the 


254     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


center  of  the  fuse  holder.  Tests  with  this  type  of  box  made 
close  to  a  source  of  power  of  2,000  kw.  failed  to  cause  any 
explosive  action  or  throwing  of  oil  under  short-circuit. 


30 


2G 


DO 


24 


22 


220 

I  18 


1C 


14 


12 


\ 


0   100   200  300  400   500  600   700  800   900  1000  1100 
Amperes 

FIG.  120. — Fusing  current  of  copper  wire  immersed  in  oil. 


FIG.  121. — Four-way  three-conductor  subway  box. 

The  boxes  are  usually  fused'for  short-circuit  and  not  for  over- 
load protection.  The  curve  shown  in  Fig.  120  shows  the  relation 
between  fusing  current  and  size  of  wire. 


DISTRIBUTION  SYSTEMS 


255 


The  first  essential  in  the  successful  operation  of  any  system 
is  continuity  of  service.  While  all  systems  are  more  or  less  sub- 
ject to  interruptions;  each  system  should  be  so  designed  that 
these  interruptions  will  be  reduced  to  a  minimum,  both  as  to 
duration  and  area  affected. 

Fig.  121  shows  a  four- way,  three-conductor  interconnecting 
junction  box  suitable  for  4,500  volts  working  pressure.  All  live 


FIG.  122. — Backview  four-way  three-conductor  subway  box. 

parts  are  mounted  in  porcelain  cells,  one  cell  taking  care  of  one 
cable  conductor.  The  bus  connections  are  made  on  the  rear 
by  copper  straps  connecting  from  the  various  studs  to  give  the 
desired  combination.  Flexible  insulated  cable  leads  are  extended 
through  the  side  of  the  box  from  the  other  stud  of  each  individual 
porcelain  cell,  thereby  making  it  possible  to  assemble  all  current- 
carrying  parts  in  the  porcelain  cells  which  are  mounted  in  a 
frame. 

Fig.  122  shows  a  rear  view  of  the  arrangement  and  electrical 
connections,  which,  when  the  box  is  assembled,  are  all  imbedded 


256     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


FIG.  123. — Two-way  three-conductor  sectionalizing  box. 


FIG.  124. — Single-pole  primary  cutout  box. 


DISTRIBUTION  SYSTEMS 


257 


in  insulating  compound.  A  two-way  sectionalizing  box  of  the 
same  construction,  built  for  three-conductor  cable  operated  at 
4,500  volts,  is  illustrated  in  Fig.  123. 

A  single-pole  primary  cutout  box  for  fusing  2,500-volt  cables 
is  shown  in  Fig.  124.  In  this  particular  design  the  ends  of  the 
cable  are  sealed  and  thoroughly  protected  from  moisture  by  a 
nipple  terminal  which  extends  through  the  wall  of  the  box  casting 
and  at  the  same  time  acts  as  a  support  for  the  spring  clip  which 
takes  the  enclosed  fuse. 


Q 

Oils 


,uia  u 


FIG.  125. — Three-pole  low-voltage  sectionalizing  box. 

Fig.  125  shows  a  three-pole  sectionalizing  box,  designed  for 
low  voltage.  The  box  may  be  arranged  for  multiple-  or  single- 
conductor  cables,  depending  upon  local  conditions.  All  cables 
whether  single  or  multiple  form  are  terminated  by  sealed  nipple 
terminal  structures;  and  disconnecting  straps  extend  between  the 
stems  in  these  nipples  so  that  all  slate  or  other  bases  may  be 
entirely  eliminated. 

In  some  installations  spare  feeders  have  been  provided  to  be 
used  in  case  of  emergency.  These  feeders  are  usually  equipped 
with  suitable  subway  boxes  so  that  they  may  be  connected  to  any 
of  the  feeders  in  trouble  and  supply  service  while  repairs  are  being 

17 


258     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

made.  Practice  seems  to  have  demonstrated  that  the  fusing 
of  mains  is  unsatisfactory;  and  in  most  installations  no  fuses  are 
used  in  the  primary  system  except  on  transformers. 

Safety  to  workmen  and  continuity  of  service  demand  the  use 
of  more  reliable  apparatus  on  an  alternating-current  system  than 
is  required  on  a  direct-current  system.  The  additional  cost  of 
sectionalizing  devices  for  the  alternating-current  underground 
system  is  small  as  compared  with  the  cost  of  the  direct-current 
system.  Load  and  service  will  be  important  factors  in  the  choice 
of  the  system. 


FIG.  126. — Manhole  service  bus. 

Service  Bus. — In  many  systems,  subway  branch  boxes  are 
used  on  the  main  cable  for  taking  care  of  the  service  connections 
to  consumers.  These  boxes  add  considerably  to  the  cost  of  the 
service  installation,  and  it  is  frequently  necessary  to  install 
additional  boxes  in  cases  where  the  number  of  outlets  in  the 
original  box  installation  is  insufficient  to  take  care  of  the  ultimate 
number  of  service  connections.  A  novel  method  of  taking  care 
of  service  connections  is  by  the  use  of  a  rubber-insulated  bus 
mounted  on  the  wall  of  the  manhole  or  distribution  hole,  as  shown 
in  Fig.  126.  In  this  type  of  construction  a  hand  splice  is  made 
on  the  main  paper-insulated  lead-covered  cable  with  rubber- 


DISTRIBUTION  SYSTEMS 


259 


insulated  lead-covered  cable;  the  lead  sheath  on  the  branch  cable 
terminating  a  short  distance  below  the  bus  rack.  Service  con- 
nections are  made  to  the  bus  with  rubber-insulated  cable  covered 
with  weatherproof  braid,  the  bus  cable  being  a  solid  conductor 
in  order  to  avoid  any  moisture  siphoning  into  the  paper  cable 
in  case  the  rubber  insulation  or  service-connection  joints  become 
defective  while  the  manhole  is  filled  with  water.  Installations 
of  this  character  have  proved  very  successful  and  have  been  in 
operation  on  220-volt  alternating-current  systems  for  a  period 
of  about  10  years  without  failure.  The  principal  advantage  with 


FIG.  127. — A.C.  and  D.C.  service  bus  with  sectionalizing  box  in  manhole. 

this  form  of  construction  is  that  the  services  of  a  lead  jointer  are 
not  required  to  make  connections  to  the  service  bus;  and  any 
number  of  services  up  to  the  capacity  of  the  bus  may  be  installed 
as  the  occasion  requires.  In  Fig.  127  is  shown  a  bus  arrangement 
as  just  described,  with  sectionalizing  boxes  on  the  secondary 
alternating-current  and  500- volt  direct-current  mains  mounted 
on  the  wall  of  the  manhole. 

Manhole  Oil  Switches. — Manhole  oil  switches  have  been  used 
quite  extensively  by  a  number  of  companies  for  disconnecting 
sections  of  cable  when  failures  occur  or  when  it  is  desired  to  work 
on  a  feeder  without  interrupting  the  service.  Multiple-pole 
hand-operated  oil  switches  of  various  capacities  and  potentials 
up  to  10,000  volts  are  in  successful  operation. 


260     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


FIG.  128. — Triple-pole  10,000-volt  manhole  oil  switch. 


FIG.  129. — Triple-pole  2,500-volt  manhole  oil.switch. 


DISTRIBUTION  SYSTEMS  261 

These  switches  are  made  for  mounting  on  flat  vertical  surfaces 
in  manholes  or  in  locations  where  there  is  danger  of  flooding. 
The  frame,  cover  and  oil  vessel  are  cast  iron,  and  by  means  of 
gaskets,  all  joints  are  made  water-tight.  The  switch  is  provided 
with  an  operating  handle  on  the  outside  of  the  frame  of  such 
design  that  the  switch  can  be  operated  with  a  hook. 

Manhole  automatic  overload  switches  are  not  recommended 
due  to  the  effect  of  low  temperature  on  the  automatic  features 
and  the  tendency  of  the  oil  to  congeal  or  thicken  at  extremely 
low  temperatures.  While  the  thickening  of  the  oil  would  not 
interfere  with  the  opening  and  closing  of  a  non-automatic  hand- 
operated  switch,  automatic  switches  must  depend  in  a  large 
measure  upon  gravity  as  the  actuating  force  in  opening,  and  the 
thickened  oil  would  have  a  tendency  to  delay  or  entirely  pre- 
vent the  opening  of  the  switch.  Further,  the  gases  generated 
by  an  automatic  switch  in  opening  the  circuit  under  short-circuit 
conditions  would,  in  spite  of  any  vent  which  might  be  provided, 
have  a  deteriorating  effect  upon  the  gaskets,  with  consequent 
danger  of  water  getting  into  the  switch  and  causing  serious 
damage.  In  Figs.  128  and  129  two  types  of  manhole  oil  switches 
are  shown. 

Alternating-current  Network  Protector. — The  use  of  the  alter- 
nating-current network  has  become  standard  practice  in  sections 
where  the  load  is  dense.  This  system  has  the  advantage  of 
permitting  the  use  of  a  smaller  number  of  transformers,  a  more 
economical  loading  of  the  transformers  and  a  greater  flexibility 
in  the  distribution  system. 

The  principal  difficulty  which  has  attended  the  interconnec- 
tion of  transformer  secondaries  has  been  the  progressive  blowing 
of  fuses  when  a  defect  developed  in  any  of  the  transformers. 
In  the  case  of  a  failure  not  only  does  the  transformer  drop  its 
load  but  the  defect  develops  into  a  short-circuit  into  which  all 
the  other  transformers  feed,  with  the  result  that  the  fuses  blow 
progressively,  starting  with  those  nearest  the  fault,  until  the  whole 
network  is  shut  down. 

To  eliminate  the  disadvantages  of  the  network  there  has  been 
developed  commercially  a  device  known  as  the  "A.C.  Network 
Protector"  designed  to  disconnect  automatically  a  faulty 
transformer. 

This  device,  which  has  no  moving  parts  to  stick  or  get  out  of 
order,  consists  of  a  small  transformer  with  primary  and  secondary 


262     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


FIG.  130. — A.C.  network  protector. 


3  WIRE  SECONDARY 


wvww 

wwvwwwwin 


Eia.  131. — Connections  of  A.C.  network  protector  for  three-wire  network, 


DISTRIBUTION  SYSTEMS  263 

windings  in  series  with  the  corresponding  windings  in  the  power 
transformer,  and  a  third  coil  wound  on  the  iron  core.  The  wind- 
ings are  so  designed  that  under  normal  conditions  the  ampere- 
turns  in  one  coil  neutralize  those  in  the  other  and  the  flux  in  the 
core  is  zero.  When  a  defect  develops  and  there  is  a  reversal  of 
current  in  the  secondary,  the  ampere-turns  add  their  effects 
together,  producing  a  heavy  flux  in  the  iron  core,  upon  which  is 
wound  the  third  coil  consisting  of  a  few  turns  of  heavy-wire 
short-circuited  through  a  V-fuse.  This  flux  sets  up  in  the  local 
circuit  a  heavy  current  which  instantly  blows  the  fuse  and 
isolates  the  faulty  transformer. 

Fig.  130  shows  the  general  appearance  of  the  protector;  and 
Fig.  131  shows  a  diagram  of  connections  for  use  on  a  three- wire 
system. 

Service  Connections  from  Underground  Mains. — The  central 
station,  in  furnishing  service  to  all  classes  of  consumers  under 
varying  conditions,  is  required  in  many  installations  to  change 
existing  overhead  services  to  an  underground  system  of  dis- 
tribution. In  some  cases  the  entire  cost  of  making  the  change 
from  overhead  to  underground  is  borne  by  the  customer,  and  in 
other  cases  the  company  bears  the  entire  cost,  the  practice  fol- 
lowed being  dependant  on  local  conditions.  It  is  the  practice 
of  some  of  the  larger  central-station  companies  to  issue  "  Rules 
and  Regulations  for  Wiring"  to  the  end  that  wiring  contractors 
doing  construction  work  for  customers  to  be  connected  to  the 
company's  mains  will  so  arrange  and  carry  out  their  work  as  to 
protect  the  interests  of  customers  and  at  the  same  time  conform 
to  such  regulations  as  experience  has  shown  are  necessary  in 
order  for  the  company  to  supply  uniform  and  satisfactory 
service. 

Wherever  it  is  desired  to  supply  current  from  underground 
mains,  the  customers'  wiring  should  terminate  and  the  meter- 
board  be  placed  at  the  front  wall  of  cellar  or  vault  nearest  the 
street.  In  some  cases  where  wiring  is  done  by  local  contractors 
and  service  is  not  actually  being  supplied  from  subways  at  the 
time  service  is  desired,  the  central  station  companies  require  an 
additional  temporary  overhead  service  to  be  installed  until  the 
underground  system  is  provided. 

Armored  Services. — In  the  early  periods  of  underground  con- 
struction, the  service  end  of  the  system  was  somewhat  neglected 
and  very  little  thought  was  given  to  the  real  importance  of  an 


264     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

ideal  service  installation.  Services  were  usually  treated  as  an 
adjunct  to  the  main  system  and  no  special  attention  was  given 
to  the  installation  as  long  as  the  connection  was  made  with  the 
property  to  be  served. 

As  the  underground  system  increased,  the  matter  of  adequate 
protection  at  the  consumer's  end  of  services  was  taken  up  by  the 
underwriters  with  the  result  that  certain  rules  and  regulations 
were  formulated  governing  the  methods  of  installation.  At 
first  many  companies  made  their  service  connections  with  lead- 
covered  cable  which  was  buried  in  the  ground.  This,  of  course, 
proved  impractical,  as  a  failure  in  the  cable  necessitated  the 
tearing  up  of  both  the  street  and  sidewalk  in  effecting  repairs. 
Another  method  of  furnishing  service  was  to  bring  the  feed  into 
a  building  at  a  street  intersection  extending  it  to  adjacent  build- 
ings through  the  various  cellars.  The  objections  to  this  type 
of  service  were  that  it  materially  increased  the  fire  hazard  and 
the  danger  of  interruptions  to  service  and  afforded  ample  means 
for  the  unscrupulous  to  obtain  current  by  theft. 

There  are  many  other  arguments  against  the  installation  of 
such  services  but  the  three  previously  mentioned  were  sufficient 
to  condemn  such  practice  and  to  show  clearly  the  need  for  indi- 
vidual service  connections.  The  next  step  was  the  installation 
of  individual  services  consisting  of  iron  pipe  or  duct  through  which 
the  cable  was  drawn.  Fire  risk,  however,  was  not  materially 
reduced  until  a  few  years  ago  when  it  was  realized  that  the  old 
type  of  terminal  block  was  inadequate.  These  terminal  blocks 
consisted  of  an  ordinary  fuse  block  which  was  not  protected 
against  dampness  nor  against  short-circuits  caused  by  accidental 
contact. 

The  writer  recalls  a  case  in  a  large  eastern  city  where  an  investi- 
gation of  service  trouble  showed  that  a  serious  short-circuit  had 
been  caused  by  the  piling  against  the  fuse  block  of  a  number  of 
steel-banded  packing  cases  filled  with  fireworks.  There  are 
still  such  services  in  existence  but  central-station  companies  are 
gradually  eliminating  them,  and  with  the  advance  in  design  of 
equipment  for  underground  services  to  meet  the  severe  operating 
conditions,  a  water-tight  service  box  with  enclosed  fuses  was 
produced.  This  equipment  was  installed  adjacent  to  the  duct 
holding  the  service  wires  which  were  carried  by  knobs  or  cleats 
to  the  service  box  where  porcelain-bushed  holes  provided  an 


DISTRIBUTION  SYSTEMS  265 

entrance  for  the  wires.     After  leaving  the  service  box,  the  main 
wire  ran  to  the  meter,  usually  located  on  the  board. 

After  a  time  the  underwriters  revised  the  rules  governing  wiring, 
condemning  the  practice  of  using  moulding  in  cellars.  This 
left  conduit  or  open  wiring  as  alternatives.  Conduit  was  more 
generally  accepted,  as  the  underwriters  had  also  ruled  that  all 
switches  and  cutouts  be  enclosed  in  iron  boxes.  With  the  in- 
creased number  of  consumers  came  an  alarming  number  of 
current  thefts,  and  the  larger  percentage  of  these  occurred  at 
services  which  were  more  or  less  obscured.  The  underground 
box  which  was  located  in  basements  afforded  a  temptation  to 
the  unscrupulous,  and  a  constant  watch  was  necessary  to  detect 


FIG.  132. — Service  box  with  meter  loop  in  wood  moulding. 

cases  of  theft.  The  plans  for  full  meter  and  service  protection 
have  been  taken  up  within  the  past  few  years  and  now  nearly 
all  of  the  larger  operating  companies  have  been  equipping 
their  underground  services  with  protective  devices.  As  most 
underground  districts  had  been  primarily  supplied  by  overhead 
services,  whose  entrance  was  usually  above  the  first  floor,  con- 
siderable expense  is  incurred  in  changing  the  location  of  meters 
from  upper  floors  to  basements.  This  involves  an  entire  new 
meterboard  and  necessary  wiring  to  connect  the  same  with  origi- 
nal distributing  centers.  The  old  method  was  as  shown  in  Fig. 
132.  This  is  inadequate  in  preventing  theft  of  current  and  does 
not  furnish  an  absolute  protection  to  the  wires.  Devices  are 
now  on  the  market  by  the  use  of  which  it  is  possible  to  get  full 


266     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

protection  from  theft  as  well  as  to  provide  an  absolutely  iron- 
clad service  at  a  very  slight  cost  over  that  of  open-wired  boards. 
Such  boards  have  many  additional  features  for  facilitating  the 
handling  and  testing  of  meters  in  service.  An  ideal  board,  as 
used  by  some  of  the  larger  operating  companies,  can  be  con- 
structed at  a  very  reasonable  cost. 

In  changing  over  from  the  old  overhead  to  new  underground 
installations,  considerable  wiring  is  necessary  to  connect  new  ser- 
vices to  points  of  distribution.  When  making  such  changes  in 
large  buildings  it  is  advisable  to  bring  all  meters  to  a  point  ad- 
jacent to  the  service.  The  following  is  an  outline  of  the  method 
employed  by  a  few  of  the  companies  making  extensive  changes 
from  overhead  to  underground  systems. 

Prior  to  starting  the  actual  work,  a  service  inspector  is  sent 
out  to  select  the  most  advantageous  point  to  make  the  service 
entrance.  In  making  this  selection  attention  must  be  given  to 
the  physical  conditions  outside  of  the  building,  such  as  location 
of  hydrants,  poles  and  other  obstructions  which  would  interfere 
with  service  pipes.  After  having  familiarized  himself  with  the 
outside,  he  selects  the  most  desirable  point  for  the  location  of  the 
service  entrance,  choosing  the  point,  where  possible,  which  is 
least  likely  to  be  obstructed  by  an  accumulation  of  material 
usually  found  in  cellars.  If  sufficient  wall  space  can  be  secured  at 
the  point  of  entrance  of  service,  the  meterboard  will  be  located 
at  that  point  unless  a  large  amount  of  interior  wiring  is  involved. 
Should  this  be  the  case,  a  meter  location  is  selected  which  will 
allow  a  more  economical  installation  by  eliminating  some  of  the 
wiring.  Such  a  case  would  be  where  there  are  a  number  of  meters 
located  at  various  points  in  a  building. 

After  the  service  pipe  is  installed,  the  interior  wiring  changes 
are  started.  Service  wire  is  pulled  in  as  the  first  step,  and  the 
service  board  is  mounted  at  the  point  selected.  The  best  form 
of  meterboard  is  constructed  of  angle  iron  made  up  in  the  form 
of  a  frame,  upon  which  may  be  mounted  backboards  to  support 
meters.  If  service  and  meters  are  to  be  located  at  the  same  point, 
an  approved  water-tight  service  box  is  bolted  to  the  side  of  the 
frame.  Service  wires  are  calked  in  the  service  pipe  with  oakum 
soaked  in  a  sealing  compound  to  exclude  gases.  Service  wires 
are  then  incased  in  a  flexible-steel  conduit,  one  end  of  which  is 
pushed  back  in  the  service  pi  pe  until  it  reaches  the  calking .  To  the 
other  end  is  attached  a  connector  which  is  made  up  to  a  fitting 


DISTRIBUTION  SYSTEMS 


267 


on  the  service  box  and  wires  are  then  soldered  into  the  service 
box.  This  method  gives  a  full  armored  protection  to  the  service 
and  is  highly  recommended  by  the  fire  underwriters. 

The  service  box  should  be  of  a  type  which  will  be  accepted  by 
the  underwriters  as  a  switch  and  cutout.  The  usual  type  of  box 
used  is  that  which  provides  for  extraction  of  fuses  when  the  cover 
is  opened.  The  load  side  of  the  service  box  is  equipped  with  a 
fitting  similar  to  that  which  receives  the  flexible  conduit  on  the 
service  side  of  box,  and  from  this  the  wires  are  carried  to  the  switch 


FIG.  133. — Apartment  house  meter  installation. 

cabinet  of  the  first  meter  and  then  on  through  the  various  cabinets 
until  the  end  of  the  bank  has  been  reached.  Each  meter  has  an 
independent  switch  and  cutout  located  between  the  service  and 
the  meter.  These  are  placed  in  a  steel  cabinet  which  is  sealed  and 
effectually  protects  the  service  against  tampering.  As  most 
companies  use  a  three- wire  bank  form  of  distributing  through 
their  underground  system,  it  becomes  necessary  to  balance 
the  load  on  each  service  as  far  as  practical,  as  many  of  the  over- 
head services  are  apt  to  be  two-wire.  It  has  been  found  that 
where  an  office  or  other  similar  building  has  a  number  of  meters, 
the  installation  may  be  practically  balanced  by  using  all  two-wire 


268     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

meters  and  connecting  these  in  staggered  position  on  a  three-wire 
service.  This  does  not  apply  to  larger  two- wire  installations, 
as  in  the  larger  installations  the  periods  of  consumption  do  not 
occur  simultaneously.  Installations  of  1,000  watts  or  larger 
should  be  changed  to  three-wire.  This  invariably  means  a 
larger  amount  of  rewiring  but  can  usually  be  done  by  extending 


FIG.  134. — Improper  meter  installation. 

the  three-wire  mains  from  the  meter  to  the  center  of  distribution 
and  there  balancing  one  subcircuit  against  another. 

In  all  such  three-wire  systems,  it  is  recommended  that  the 
neutral  wire  be  made  solid  from  the  manhole  or  transformer 
to  the  point  of  distribution.  Solid  or  dummy  fuses  should  be 


DISTRIBUTION  SYSTEMS  269 

installed  in  the  service  box  and  so  arranged  as  not  to  be  removed 
when  cover  is  opened  and  other  fuses  are  extracted.  This  has 
one  distinct  advantage  in  changeover  jobs,  especially  where  the 
old  jobs  have  had  a  grounded  service.  Such  services  are  apt  to 
have  local  grounds  on  the  building,  and  in  changing  over  if  no 
secondary  ground  was  on  the  original  service  these  local  grounds 
are  apt  to  appear  on  the  live  leg  of  the  distributing  main  and  blow 
fuses.  The  current  will  then  find  a  path  back  through  load,  and 
owing  to  the  resistance  of  the  ground,  will  probably  cause  a  fire. 
With  the  solid  neutral,  this  difficulty  may  be  overcome  safely  by 


FIG.  135. — Iron-clad  meter  installation. 

transposing  the  circuit  wires  on  which  the  ground  appears.  The 
best  form  of  neutral  wires  to  install  from  street  to  service  box  is 
a  stranded  bare  tinned  copper  of  not  less  capacity  than  that  of 
the  outside  wires,  and  in  no  case  should  this  be  less  than  No.  6 
B.  &  S.  gage.  Fig.  133  shows  a  model  service  installation  for 
apartment  houses  and  large  buildings.  The  service  is  installed 
in  iron  conduit  from  the  manhole  to  the  service  box  as  described 
before.  This  installation  is  equipped  with  meter  protective  and 
testing  devices  in  which  are  also  incorporated  consumer's  fuses 
and  switch  control.  This  represents  an  iron-clad  installation  in 
which  there  are  no  wires  or  current-carrying  parts  exposed  from 
the  manhole  to  the  first  point  of  distribution.  The  features  of 
the  testing  devices  are  that  a  meter  may  be  tested,  replaced  if 
necessary,  or  repaired,  without  interruption  of  service  to  the  con- 
sumer. Shunting  arrangements  are  made  by  which  meters  may 


270     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

be  entirely  isolated  from  the  line  for  purpose  of  repairs  or  changes, 
thus  eliminating  danger  to  the  operator.  It  is  also  possible  to 
discontinue  service  for  non-payment  or  other  causes  and  lock 
same  out  until  such  time  as  it  becomes  desirable  to  reinstate 
service.  This  is  very  convenient  where  there  is  a  change  of 
tenants  and  it  is  desirable  to  make  a  meter  transfer.  Fig.  134 
shows  a  job  which  was  changed  over  and  shows  the  hazardous 
condition  of  wires  both  from  a  fire  and  theft  of  current  standpoint. 
Many  old  installations  have  reached  such  a  condition  and  should 
be  rebuilt. 

Fig.  135  shows  a  service  equipped  with  armor.  Such  in- 
stallations as  are  shown  in  Fig.  135  can  be  made  for  less  than 
$2.50  per  meter,  which  includes  complete  outfit  installed  as 
shown. 

Protection  of  Transmission  Systems. — The  growth  in  the 
central-station  industry  and  the  use  of  high-voltage  transmission 
cable  has  brought  about  numerous  problems  which  have  made  it 
necessary  to  resort  to  various  methods  for  protection  of  the 
system. 

The  increase  in  size  of  generating  and  substation  equipment, 
together  with  the  increase  in  size  and  voltage  of  the  connected 
cables,  has  made  it  exceedingly  difficult  to  handle  short-circuit- 
ing values.  The  change  from  engine-driven  units  of  compara- 
tively small  capacity  and  slow  speeds  to  turbine-driven  units  of 
large  capacity  and  high  speeds  is  perhaps  one  of  the  largest 
factors  in  the  problem. 

Experience  has  shown  that  no  single  part  of  an  electrical  sys- 
tem is  free  from  the  possibility  of  injury,  and  that  it  is  incumbent 
upon  operating  and  designing  engineers  to  protect  their  systems 
as  far  as  possible  from  such  occurrences  through  the  use  of  pro- 
tective devices  suitably  designed  to  afford  such  protection. 

Relays. — Oil-break  switches  and  carbon-break  circuit-breakers 
are  commonly  used  to  open  electrical  circuits  at  some  given 
overload  and  on  short-circuit.  To  secure  additional  protection 
under  a  variety  of  abnormal  conditions  or  to  provide  for  a  certain 
predetermined  operation  or  sequence  of  operation,  relays  may  be 
advantageously  employed.  The  connections  between  the  relays 
and  circuit-opening  devices  are  usually  electrical  and  are  ex- 
tremely flexible  since  they  admit  of  the  use  of  a  number  of  devices, 
each  having  a  different  function,  with  a  single  oil  switch  or  circuit- 


DISTRIBUTION  SYSTEMS 


271 


breaker  as  well  as  with  one  or  more  switches  to  secure  the  desired 
operation  or  protection. 

Relay  protection  for  transmission  lines  varies  with  the  type 
and  method  of  operating  different  systems,  but,  in  general,  either 
instantaneous,  inverse  time-limit  or  definite  time-limit  types  of 

3  Wire  Feeder  D.C.Feeder    Feeders       Motors    Lighting 


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FIG.  136. — Diagram  of  modern  power  house  wiring  and  busses  showing 

location  of  relays.1 

relays  have  been  used  according  to  engineering  judgment.  The 
arrangement  of  relays  on  a  feeder  or  transmission  line  must  be 
such  that  the  occurrence  of  a  short-circuit  between  any  two  wires 
will  open  the  breaker.  On  single-phase  circuits  one  relay  is 

i  G.  E.  Co.  Bulletin  4857-A. 


272     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

sufficient  to  accomplish  this.  One  of  the  fundamental  condi- 
tions beginning  to  be  more  fully  appreciated  by  engineers  is  that 
each  particular  line  should  be  treated  individually  with  respect 
to  its  relay  setting  instead  of  having  a  certain  definite  setting 
for  the  relays  of  all  lines  in  a  given  class. 

In  order  to  determine  the  proper  setting  of  instantaneous  over- 
load, time-limit  and  inverse  time-limit  relays  which  are  more 
commonly  used  on  a  system  of  distribution,  it  is  necessary  to 
know  the  characteristics  of  the  system  as  well  as  the  character- 
istics of  the  generators,  automatic  apparatus,  circuit-breakers, 
regulators,  etc. 

In  systems  operating  radial  feeders,  with  each  feeder  connect- 
ing to  only  one  substation  and  not  operating  in  parallel  at  sub- 
station ends,  reasonably  satisfactory  service  has  been  rendered 
by  the  type  of  relays  referred  to. 

In  systems  operating  ring  systems  of  feeders,  or  radial  feeders 
with  several  substations  in  tandem  on  a  single  feeder,  where 
selective  action  is  required  in  order  to  prevent  interruption  of 
service  from  all  stations  between  a  fault  and  the  source  of  power, 
satisfactory  results  have  rarely  been  continuously  attained  with 
any  of  the  types  of  relays  mentioned. 

In  Fig.  136  is  shown  a  one-line  diagram  which  will  be  of  assist- 
ance in  making  a  selection  from  the  various  types  of  relays  to 
meet  the  requirements  of  power-house  and  substation  layouts. 

It  should  be  noted  that  the  selection  of  relays  to  meet  actual 
operating  conditions  is  an  important  problem  and  should  receive 
careful  attention  when  a  new  system  is  being  laid  out  or  exten- 
sions are  being  made  to  a  system  already  installed. 

The  successful  operation,  selective  cutting  out  of  trouble,  and 
the  continuity  and  safety  of  service,  depend  entirely  on  the  opera- 
tion of  automatic  oil  switches  and  circuit-breakers,  which  in  turn 
must  be  tripped  by  means  of  relays.  There  are  many  types  of 
relays,  each  type  designed  to  perform  certain  functions,  and 
before  any  of  these  types  are  installed,  a  careful  study  should  be 
made  of  the  conditions  under  which  they  must  operate. 

Current-limiting  Reactance  Coils. — When  short-circuits  occur 
in  the  cable  system,  a  tremendous  current  flow  is  set  up  which 
reaches  its  maximum  during  the  first  cycle.  When  it  is  realized 
that  for  this  first  cycle  every  generator  connected  to  the  bus  is 
able  to  assume  a  short-circuiting  value  of  at  least  ten  times  its 
rated  capacity,  it  is  readily  seen  that  heavy  stresses  are  imposed 


DISTRIBUTION  SYSTEMS 


273 


on  the  switches,  cables  and  apparatus.  The  stresses  on  the 
feeder  switches  at  such  times  are  enormous,  and  it  has  become 
necessary  of  late  years  to  lock  knife  switches  in  position  and  to 
take  steps  to  protect  the  oil  switches  against  these  effects.  To 
relieve  this  condition  and  protect  the  system,  various  types  of 
apparatus  have  been  employed.  The  use  of  reactances,  both 
external  and  internal,  on  generators,  as  well  as  on  the  bus  and 
feeder  circuits,  has  perhaps  been  one  of  the  most  effective  means 
of  protecting  the  central  station  and  cable  system. 


FIG.  137. — Cast-in-concrete  type  of  current-limiting  reactance. 

In  general,  it  may  be  said  that  in  stations  of  large  capacity, 
external  current-limiting  reactance  coils,  in  one  form  or  another, 
have  become  a  necessity  for  the  protection  of  oil  switches  and 
service.  Local  conditions  will  govern  the  type  of  reactances  to 
be  used,  but  wherever  possible,  it  is  now  generally  admitted  that 
the  best  protection  to  service  is  obtained  from  the  use  of 
reactances  on  the  individual  feeder  circuits. 

A  large  company,  which  has  recently  completed  the  installation 
of  5  per  cent,  reactance  coils  on  all  13,200-volt,  60-cycle  feeders 
has  noticed  a  very  material  improvement  in  the  selective  opera- 
tion of  relays,  with  the  resultant  benefit  to  the  system.  Short- 
circuits,  which  formerly  caused  an  interruption  to  service  on 
several  multiple  feeders,  have  now  become  minimized  to  such  an 

18 


274     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

extent  that  only  the  short-circuited  feeder  releases  and  the  syn- 
chronous apparatus  in  the  system  is  not  affected. 

No  combination  of  generator  and  bus  reactances  will  give  this 
protection  to  service,  as  their  installation  is  intended  primarily 
to  protect  station  apparatus.  The  percentage  of  reactances  to 
be  used  is  still  an  open  question  and  cannot  be  standardized  as  it 
depends  largely  upon  operating  conditions.  The  practice  is  to 
have  a  total  reactance  of  8  to  12  per  cent,  on  generator  circuits  and 
about  2  to  5  per  cent,  on  feeder  circuits. 

Current-limiting  reactances  should  be  of  the  air-core  type,  and 
their  capacity  should  correspond  to  the  full -load  capacity  of  the 


FIG.  137a. — Semi-porcelain-clad  type  of  current-limiting  reactance. 

line  which  they  are  intended  to  protect.  They  are  generally 
built  with  a  core  of  non-magnetic  material  such  as  wood,  concrete, 
porcelain,  or  of  several  such  materials  in  combination.  Two  types 
of  feeder  reactance  coils  are  illustrated  in  Figs.  137  and  137a.  In 
general,  they  are  so  bulky  that  it  is  difficult  to  find  room  for  their 
installation  in  a  station  already  built.  In  some  cases  separate 
structures  adjacent  to  the  generating  station  or  the  switch-house 
have  been  found  necessary  for  their  proper  housing.  When  these 
reactance  coils  are  properly  constructed  and  placed,  their  in- 
stallation involves  no  additional  hazard. 

Selective  Fault  Localizer. — The  localizer  is  designed  primarily 
to  indicate  on  which  feeder  a  ground  occurs  when  there  are  a 
number  of  radial  lines  connected  to  a  high-tension  busbar.  The 
device  necessitates  a  relay  for  each  feeder.  One  of  these  relays 
is  shown  in  Fig.  138.  They  are  connected  to  the  respective  cur- 
rent transformers  of  the  lines  on  which  it  is  desired  to  localize, 
in  such  a  manner  that  all  load  currents  are  balanced  out,  as  shown 


DISTRIBUTION  SYSTEMS 


275 


in  Fig.  139.     The  various  relays  are  interconnected  in  such  a  way 
that  only  the  relay  on  the  grounded  line  is  operative.     All  the 


FIG.  138. — Relay  for  localizer  of  faulty  feeders. 

3>4> STATION    BUS. 


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FIG.  139. — Connections  of  feeder-localizer  apparatus  as  applied  to  a  three- 
phase  system. 

other  relays  are  rendered  non-operative  by  balancing  the  mag- 
netic pulls,  one  against  the  other  in  successive  pairs.     When  a 


276     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


ground  occurs  on  a  high-tension  system,  the  proper  relay  operates 
and  illuminates  its  signal  lamp  to  indicate  the  grounded  feeder. 
This  device  is  used  as  an  auxiliary  appliance  to  the  arcing- 
ground  suppressor.  When  the  two  devices  are  used  in  combina- 
tion, it  is  possible  to  have  a  ground  occur  upon  a  system  without 
interrupting  the  service.  As  soon  as  a  ground  develops,  the 
localizer  operates  being  followed  immediately  by  the  arcing- 
ground  suppressor,  which  automatically  cuts  out  the  arc  to 
ground. 


FIG.  140. — Three-phase  electro-magnetic  selective  relay  for  arcing-ground 

suppressor. 

If  this  arc  were  allowed  to  play  for  any  length  of  time  it  would 
develop  into  a  short-circuit  in  the  cable  system.  With  the  ac- 
cidental arc  suppressed,  the  station  operator  can  now  substitute  a 
good  cable  for  the  faulty  one  and  open  the  switch  of  the  arcing- 
ground  suppressor,  thus  clearing  the  system. 

Arcing-ground  Suppressor. — There  are  two  essential  parts 
to  the  arcing-ground  suppressor:  first,  a  selector  of  a  grounded 
phase,  Fig.  140;  and  second,  a  single-phase  switch  between  each 
phase  of  the  busbar  and  ground.  When  an  accidental  ground 
takes  place  in  the  system,  the  potential  of  that  phase  to  ground  is 
reduced,  which  causes  the  selector  to  pick  out  and  operate  the 
corresponding  single-phase  switch.  This  single-phase  switch 


DISTRIBUTION  SYSTEMS  277 

extinguishes  the  arc  no  matter  where  it  occurs  on  the  system, 
and  thus  stops  further  development  of  the  trouble  as  well  as 
preventing  surges  which  accompany  an  arcing  ground.  When  a 
substitute  cable  is  switched  in,  the  faulty  cable  is  taken  out  and 
then  the  switch  of  the  arcing-ground  suppressor  is  opened.  The 
single-phase  switches  are  designed  with  two  contacts  in  series, 
with  resistances  between  contacts.  A  circuit  is  never  made  nor 
broken  without  this  resistance  in  series  to  damp  out  oscillations. 

Grounded-neutral  Systems. — Some  companies  in  order  to 
gain  additional  protection  operate  on  a  grounded-neutral  system, 
while  others  resort  to  the  use  of  various  types  of  arcing-ground 
suppressors.  The  practice  of  grounding  the  neutral  on  trans- 
mission systems  has  not  so  far  been  standardized,  and  it  is  the 
practice  of  some  companies  to  operate  with  the  neutral  free  from 
ground,  while  others  ground  the  neutral  through  varying  amounts 
of  resistance,  and  in  still  other  cases  the  neutral  is  grounded 
without  any  resistance. 

In  a  system  with  the  neutral  ungrounded,  when  one  conductor 
becomes  grounded,  the  arc  may  establish  and  extinguish  itself 
in  rapid  succession,  creating  an  arcing  ground  .which  would  have 
been  eliminated  if  the  neutral  had  been  grounded.  The  presence 
of  an  arcing  ground  of  high-frequency  oscillation  is  liable  to 
create  surges  destructive  to  the  cable  and  apparatus.  Where 
the  neutral  is  grounded  through  a  resistance,  the  high-frequency 
voltage  between  two  of  the  conductors  and  ground  is  minimized 
when  the  other  conductor  is  grounded.  This  same  result  is 
accomplished  also  in  an  ungrounded  system  by  the  use  of  an 
arcing-ground  suppressor,  when  the  faulty  conductor  is  grounded 
through  the  suppressor  switch.  This  operation  is  accomplished 
in  a  fraction  of  a  second  and  eliminates  the  arcing  ground  and 
with  it  the  attending  high-frequency  voltage,  thus  leaving  the 
cable  with  line  voltage  between  the  other  two  conductors  and 
ground.  This  operation  causes  no  interruption  to  the  system, 
and  the  faulty  feeder  may  be  taken  out  of  service  at  leisure. 
Another  feature  of  the  arcing-ground  suppressor  is  that  in  cases 
of  accidental  contacts  with  the  bus  by  employees  working  in 
the  vicinity,  the  suppressor  may  act  with  sufficient  promptness 
to  prevent  fatal  accidents.  A  number  of  instances  of  this  kind 
have  been  reported  to  the  writer. 

In  the  grounded  system  the  voltage  to  ground  decreases  as  the 
resistance  between  the  neutral  and  ground  decreases,  and  in- 


278     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

creases  as  the  generator  capacity  increases.  It  is  necessary  to 
decrease  the  resistance  in  the  neutral  as  the  capacity  of  the 
system  increases  in  order  to  confine  the  voltage  strains  to  the  same 
limits.  But  since  the  current  that  can  flow  over  a  short-circuit 
between  one  conductor  and  ground  may  be  limited  by  the 
resistance  in  the  neutral,  most  of  the  companies  using  the  resist- 
ance prefer,  in  case  one  conductor  becomes  grounded,  to  use 
such  resistance  as  will  allow  the  necessary  current  to  flow  to 
operate  the  relays  properly  without  regard  to  the  voltage  rise. 

In  expanding  the  idea  of  decreasing  the  resistance  between  the 
neutral  and  ground  in  order  to  minimize  the  voltage  strains  to 
ground,  one  large  company,  after  operating  with  the  neutral, 
grounded  through  a  resistance  for  several  years,  has  decided  to 
ground  the  neutral  without  resistance.  Under  this  condition, 
when  one  conductor  becomes  grounded,  the  current  on  that  con- 


fYtfCK  INSULATION 

'rHfv*  INSULATION 


INSULATION 
TWISTED  f*Af>e*  LflTKRII-S. 


FIG.  141. — 350,000  c.m.  13,200-volt  split-conductor  paper  insulated-sector 

cable. 

ductor  approximates  that  flowing  over  a  short-circuit  between 
conductors,  which  will  cause  the  selective  relays  to  operate  in 
the  same  manner  as  when  a  short-circuit  occurs  between  con- 
ductors, the  condition  for  which  the  relays  are  set. 

There  is  considerable  difference  of  opinion  regarding  the 
advisability  of  grounding  the  neutral  and  the  relative  advantages 
and  disadvantages  resulting  therefrom.  For  more  detailed 
information  regarding  the  practice  of  grounding  the  neutral  and 
the  operation  of  arcing-ground  suppressors,  the  reader  is  referred 
to  the  Proceedings  of  the  American  Institute  of  Electrical 
Engineers. 

Merz  System  of  Cable  Protection. — The  Merz  system  of  cable 
protection  consists  of  the  usual  equipment  of  current  trans- 
formers, relays  and  oil  switches,  but  the  current  transformers  at 


DISTRIBUTION  SYSTEMS 


279 


Bus  Bar 


.=.  Tripping 
Battery 


Divided  Main 
Conductor 


opposite  ends  of  the  transmission  line  are  connected  in  opposition 
through  an  independent  pilot  cable  paralleling  the  main  trans- 
mission line.  By  this  arrangement  no  current  will  flow  through 
the  secondaries  of  the  current  transformers  so  long  as  the  same 
amount  of  current  flows  in  the  same  direction  in  each  of  their 
primaries;  but  should  there  be  a  breakdown  of  the  cable  insula- 
tion between  the  transformers,  conditions 
would  be  so  changed  that  current  would 
flow  through  the  secondaries  of  both  trans- 
formers, actuate  the  relays  and  open  the  oil 
switches  at  both  ends  of  the  line.  There 
would  then  be  remaining  in  service  the 
transmission-ring  system  with  one  section 
cut  out  but  with  a  service  to  all  substa- 
tions unimpaired  and  supplied  through  the 
lines  remaining  in  service. 

The  disadvantages  of  this  method  of  pro- 
tection are  the  complications  of  the  addi- 
tional three-conductor  pilot  cable  and  the 
fact  that  a  short-circuit  of  the  control 
cable  would  operate  the  relays  of  the  sec- 
tion of  the  main  cable  it  protects. 

The  objections  to  the  installation  of  the 
pilot-wire  cable  and  the  difficulties  en- 
countered in  its  maintenance  have  led  to 
the  present  development  of  split-conductor 
cables  in  the  application  of  the  balanced 
system  of  protection  to  transmission  lines. 
In  Fig.  141  is  illustrated  a  sector  type  of 
split-conductor  cable  as  manufactured  and 
now  used  in  this  country  by  several  large 
central-station  companies. 

This  balanced  system  of  protection  has 
been  developed  and  patented  by  Mr.  J.  C. 
Hunter,  of  the  firm  of  Merz  &  McLellan. 
In  the  balanced-current  method  of  con- 
trol in  connection  with  main-line  conductors,  each  conductor  is 
divided  into  two  parts  of  equal  resistance  and  carrying  capacity. 
The  currents  in  these  conductors  are  balanced  against  each  other 
in  the  usual  manner  to  operate  secondary  relays,  thereby  avoid- 
ing all  necessity  of  using  the  pilot  cable.  A  method  of  connect- 


.=.  Tripping 
J  .  ^    Battery 


Main 
Swltc 

Bus  Bar 

FIG.  142.— One-line 
diagram,  illustrating 
the  split-c onductor 
scheme  of  feeder  pro- 
tection. 


280     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

ing  a  split-conductor  scheme  of  feeder  protection  is  shown  in  Fig. 
142.  The  general  adoption  of  this  type  of  cable  in  many  trans- 
mission undertakings  abroad  indicates  that  the  advantages  to  be 
derived  from  its  use  are  considered  as  effecting  material  im- 
provements in  the  reliability  of  service  and  are,  therefore,  worthy 
of  recognition  in  American  practice. 


CHAPTER  IX 
ELECTROLYSIS 

General. — Electrolysis  as  here  referred  to  is  the  chemical 
decomposition  of  metallic  structures  by  electric  currents.  Soil, 
when  entirely  dry,  has  a  very  high  resistance,  but  under  normal 
conditions  street  soils  contain  varying  amounts  of  water-holding 
salts  in  solution,  thus  making  the  earth  a  fair  conductor  of  elec- 
tricity. The  specific  resistance  of  soils  varies  widely,  ranging 
from  a  few  hundred  ohms  per  cm.3  for  moist  soils  to  25,000  or 
30,000  ohms  per  cm.3  in  the  case  of  dry  sandy  soils. 

Since  it  is  to  a  large  extent  the  moisture  which  makes  soil  a 
conductor,  the  passage  of  currents  through  the  earth  is  by  elec- 
trolytic conduction,  and  is  accompanied  by  a  decomposition  of  the 
metal  at  the  point  where  the  current  leaves  an  underground  struc- 
ture to  take  a  path  of  lower  resistance  through  the  earth.  This  is 
true  of  both  direct  and  alternating  currents  except  that  the  rate 
of  decomposition  by  an  alternating  current  is  only  about  1  per 
cent,  of  that  caused  by  a  direct  current  of  the  same  value. 

The  rate  of  oxidation  is  proportional  to  the  current  strength, 
and  from  a  consideration  of  the  theoretical  amount  of  metal 
changed  into  the  oxide  it  will  be  seen  that  even  though  the  de- 
composition of  underground  structures  does  not  follow  the 
electrochemical  law  exactly,  the  amount  of  metal  oxidized  in  a 
year  is  very  considerable.  The  constant  for  iron  (converted  into 
the  ferrous  condition)  is  1.042,  and  for  lead  3.858  grams  per 
amp-hr.  The  amount  of  iron  oxidized  in  a  year  will  be  1.042  X 
8,760  X  0.002205  =  20.2  Ib.  per  amp.  The  amount  of  lead  will 
be  3.858  X  8,760  X  0.002205  =  74.1  Ib.  per  year  per  amp. 

Either  more  or  less  (but  generally  less)  than  this  theoretical 
amount  is  realized  under  actual  conditions,  depending  upon 
soil  conditions. 

The  effects  of  electrolytic  action  would  be  far  less  serious  if 
this  loss  of  metal  were  distributed  evenly  over  the  structure, 
but  this  unfortunately  is  not  the  case.  Actually  the  currents 
discharge  from  a  number  of  small  areas,  causing  pitting.  Thus 

281 


282     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

the  usefulness  of  a  structure  may  be  destroyed  by  being  badly 
corroded  in  a  few  spots  while  the  amount  of  oxidation  over  the 
rest  of  its  surface  is  negligible. 

Electrolytic  corrosion  in  most  cases  is  caused  by  stray  currents 
which  have  leaked  from  grounded  electrical  systems.  The 
stray  currents  from  grounded  telegraph  and  telephone  lines  and, 
in  general,  from  direct-current  distribution  systems  are  so  small 
as  to  be  negligible. 

Railway  return  conductors,  since  they  carry  comparatively 
heavy  curents,  are  the  only  sources  of  stray  currents  which 
need  be  considered  in  connection  with  the  problem  of  electrolysis. 


VOl.  TS 


FIG.  143.  —  Diagram  showing  stray  railway  currents  with  assumed  distribu- 
tion of  potentials  caused  by  these  currents. 

Trouble  from  electrolysis  followed  close  upon  the  introduction 
of  electric  traction.  In  the  early  days  of  the  industry  engineers 
did  not  foresee  the  danger,  and  very  little  attention  was  paid  to 
the  proper  bonding  of  the  track  return,  with  the  result  that  the 
greater  part  of  the  return  current  left  the  rails  to  take  a  path  of 
lower  resistance  through  the  earth  or  along  adjacent  metallic 
structures.  Even  after  the  necessity  of  proper  bonding  came  to 
be  realized,  a  considerable  part  of  the  current  returned  to  the 
negative  bus  through  the  earth.  Fig.  143  shows  a  simple  trolley 
system  in  which  the  return  current  divides,  part  returning  along 
the  rail,  part  through  the  earth,  and  part  along  the  iron  water 
main.  The  greatest  damage  to  the  main  will  occur  at  A  where 
the  current  leaves  the  pipe  to  pass  through  the  ground  to  the 


ELECTROLYSIS  283 

negative  bus.  Corrosion  will  also  occur  at  the  joints,  due  to  the 
fact  that  where  the  joint  resistance  is  high  the  current  will  by- 
pass the  joint  through  the  earth,  returning  to  the  pipe  on  the 
other  side. 

Before  attempting  to  utilize  any  of  the  systems  for  the  mitiga- 
tion of  electrolysis,  attention  should  be  given  to  the  matter  of 
proper  rail  bonding  and  the  limiting  of  the  distance  between 
substations. 

Rails  may  be  bonded  by  the  installation  of  copper  ribbon  or 
wire  soldered  or  brazed  to  the  webs  of  the  rails  or  by  welding 
together  the  ends  so  as  to  make  practically  a  continuous  rail. 

In  many  installations  not  only  are  the  separate  rail  sections 
bonded  but  the  two  rails  or  (in  the  case  of  a  double-track  road) 
all  four  rails  are  electrically  connected. 

The  method  of  bonding  rails  by  the  use  of  a  welding  outfit 
has  been  used  to  a  considerable  extent  and  is  apparently  satisfac- 
tory since  it  provides  mechanical  reinforcement  in  addition 
to  a  good  electrical  connection. 

A  great  deal  of  attention  has  been  given  to  the  matter  of  rail 
bonding;  and  since  the  methods  in  use  to-day  produce  bonds  which 
show  a  conductivity  of  about  80  per  cent,  as  compared  with  an 
equivalent  continuous  rail,  it  is  doubtful  whether  any  further 
relief  for  electrolytic  conditions  can  be  expected  from  attempts 
to  improve  upon  the  present  bonding  methods. 

The  number  of,  and  the  distance  between,  stations  or  substa- 
tions which  supply  a  railway  line  will  govern  to  a  very  large 
extent  the  amount  of  current  which  will  leak  to  pipe  lines  or 
other  foreign  structures. 

Where  too  small  a  number  of  stations  are  used  to  supply 
a  railway  line,  the  return  current  to  the  negative  bus  will  be  large 
and  the  distance  between  stations  comparatively  long.  These 
two  factors  bring  about  the  condition  of  excessive  voltage  drop 
along  the  rails  and  aggravate  the  tendency  of  current  to  return 
through  the  ground. 

American  engineers  apparantly  did  not  have  as  thorough  a 
grasp  of  the  situation  as  did  engineers  on  the  Continent.  As 
soon  as  the  problem  of  electrolysis  became  serious  in  Europe, 
regulations  were  adopted  limiting  the  voltage  drop  between 
any  two  points  in  the  track  to  about  7  or  8  volts.  These  regula- 
tions forced  railway  companies  to  install  better  bonds,  to  limit 
the  distance  between  stations  and,  in  some  cases,  to  install 


284     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

insulated  return  feeders,  with  the  result  that  troubles  from 
electrolytic  corrosion  disappeared  almost  entirely. 

American  practice,  on  the  other  hand,  has  not  sought  to 
remove  the  underlying  causes  of  electrolysis  but  has  attempted 
merely  to  relieve  acute  local  conditions.  The  measures  adopted 
in  this  country,  in  addition  to  track  bonding,  have  consisted 
of  "pipe  drainage"  or  bonds  to  other  systems.  It  must  not  be 
inferred  that  the  drainage  system  is  inherently  bad,  for  up  to 
the  present  time  it  has  undoubtedly  relieved  acute  cases  of  elec- 
trolysis and  has  apparently  imposed  no  serious  hardship  on  the 
owners  of  structures  tied  in  by  the  bonds.  In  spite  of  the  results 
obtained  by  the  drainage  system,  it  does  not  cure  electrolysis 
nor  remove  the  fundamental  causes,  and  it  is  to  be  regretted 
that  the  large  investment  necessary  for  the  development  of  an 
adequate  bonding  system  was  not  used  to  develop  some  positive 
cure  such  as  the  return-feeder  system.  It  is  true  that  where 
a  large  system  has  adopted  drainage  bonds  as  a  remedy  the 
cost  of  a  change  to  the  return-feeder  system  would  be  almost 
prohibitive;  and  the  writer  believes  that  in  most  cases  the  drain- 
age system  is  very  nearly  as  satisfactory  a  remedy  as  the  return- 
feeder  system,  provided  careful  and  systematic  tests  are  made. 

Drainage  Systems. — The  aim  in  all  drainage  systems  is  to 
lower  the  potential  of  the  structure  with  respect  to  the  earth 
by  draining  off  the  current  through  metallic  bonds.  The  proper 
location  for  these  bonds  is  determined  by  tests,  and  the  drainage 
conductors  are  installed  at  points  where  the  structure  is  danger- 
ously positive  to  the  adjacent  track.  The  current  is  drained 
either  to  the  track  or  else  direct  to  the  negative  railway  bus  by 
means  of  return  feeders.  If  all  the  current  could  be  drained  from 
the  structure  by  means  of  bonds,  the  bonding  system  would  be 
an  excellent  means  of  relieving  conditions  on  the  particular 
structure  so  drained.  The  problem  is  not  solved,  however,  by 
indiscriminate  bonding.  Drainage  of  any  one  structure  lowers 
its  potential  with  respect  to  neighboring  structures,  with  the 
result  that  the  latter  will  drain  through  the  ground  to  the  bonded 
pipe  line.  It  is,  therefore,  clear  that  while  bonding  may  clear  up 
conditions  in  one  place  it  may  work  to  the  injury  of  structures 
not  tied  into  the  network. 

Where  the  drainage  bonds  are  so  installed  that  a  pipe  line  be- 
comes a  parallel  return  for  the  track  circuit,  it  is  practically  im- 
possible to  control  the  amount  of  current  carried  on  the  pipe  line, 


ELECTROLYSIS  285 

and  serious  overheating  may  result.  If  the  pipe  joints  offer  a 
high  resistance,  the  current  will  leak  around  the  joint  and  corrode 
the  metal  at  the  point  where  the  current  passes  into  the  soil.  The 
use  of  such  bonds  to  a  pipe  line  where  high-resistance  joints  occur 
may  place  the  line  in  a  worse  condition  than  would  obtain  in  the 
absence  of  any  bonds  at  all.  In  the  unbonded  condition  the 
total  yearly  loss  of  metal  would  be  greater  but  under  some  condi- 
tions of  bonding  the  action  is  localized  and  intensified  so  as  to 
cause  the  structure  to  corrode  through  in  a  number  of  places. 

In  addition  to  the  above  objection,  the  system  is  not  permanent 
in  that  any  radical  change  in  conditions  will  necessitate  a  complete 
change  in  the  bonding  system  in  the  locality  affected. 

In  any  system  where  the  pipe  parallels  the  track,  the  current 
will  divide  approximately  in  inverse  proportion  to  the  resistance; 
and  in  such  a  system,  when  the  current  carried  by  the  pipe  be- 
comes excessive,  the  current  on  the  pipe  can  be  decreased  only  by 
an  increase  in  rail  conductivity.  This  method  requires  the  use 
of  a  very  costly  installation  of  copper  as  an  auxiliary  return. 

Excessive  currents  on  pipe  lines  are  a  source  of  danger  not  only 
to  the  pipe  itself  but  to  buildings  into  which  service  connections 
are  run.  There  are  cases  on  record  of  very  serious  overheating 
of  pipe  connections  inside  buildings.  However,  this  danger  is 
remote,  and  is  due  not  to  the  use  of  bonds  but  to  the  installation 
of  bonds  in  the  wrong  place. 

Probably  the  best  way  to  drain  a  pipe  line  is  by  the  installation 
of  insulated  drainage  feeders  running  from  the  negative  bus  in  the 
station  to  various  points  on  the  structure.  It  is  possible  by  the 
use  of  such  a  system  to  control  very  closely  the  distribution  of 
current  on  the  pipe  line  by  varying  the  resistance  of  the  drainage 
leads. 

This  method  is  better  than  the  preceding,  but  all  drainage  sys- 
tems have  the  disadvantage  that  with  growth  in  the  railway 
system  it  may  be  necessary  to  drain  very  large  currents  from  pipe 
lines,  and  that  in  many  cases  the  trouble  is  merely  transferred 
from  one  area  to  another. 

Numerous  attempts  have  been  made  to  protect  pipe  lines  from 
the  effects  of  electrolysis  by  means  other  than  the  use  of  bonds. 

Protective  Coatings. — Protective  coatings  in  the  form  of 
paint,  dips  of  asphalt,  coal  tar  or  pitch,  and  wrappings  of  paper 
or  cambric  have  been  used  to  some  extent,  but  tests  have  failed 
to  show  that  any  one  method  is  universally  satisfactory. 


286     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

\ 

It  is  difficult  to  apply  any  coating  so  as  to  obtain  a  uniform 
smooth  surface  free  from  pinholes  or  bare  spots.  Where  these 
exist,  a  pipe  line  may  fail  much  more  quickly  than  where  the  pipe 
is  uncoated  due  to  the  fact  that  corrosion  will  be  localized  in 
a  small  number  of  areas,  the  effect  of  electrolytic  action  being 
intensified. 

Even  if  the  coating  is  very  carefully  applied,  it  is  likely  to  be 
scratched  in  handling;  and  after  the  pipe  is  laid,  blisters  often 
form  on  the  coating  and  expose  the  metal  to  corrosion. 

Insulation  in  the  form  of  wrappings  of  cloth  or  paper  fail  in 
most  instances  because  they  are  not  entirely  impervious  to  mois- 
ture. The  coating  becomes  damp  in  spots  and  affords  a  conduct- 
ing path,  with  the  result  that  the  pipe  fails. 

Dips  consisting  of  coal  tar  or  pitch  which  are  applied  hot  and 
allowed  to  cool  and  harden  on  the  pipe  surface  are  very  likely  to 
develop  cracks.  It  is  possible  to  make  coatings  absolutely  im- 
pervious, but  only  at  an  excessive  cost.  Such  an  installation  re- 
quires the  construction  of  a  trench  in  which  the  pipe  is  laid,  the 
pitch  being  poured  in  and  allowed  to  cool.  This  method  is 
not  recommended  except  in  special  cases  where  continuity  of 
service  is  of  such  importance  as  to  make  the  cost  of  the  installa- 
tion a  minor  consideration. 

Cement  coverings,  even  when  several  inches  in  thickness, 
will  not  afford  certain  protection  because  concrete  is  not  imper- 
vious to  moisture,  and  moist  concrete  is  a  fairly  good  conductor. 

Electrolytic  conditions  on  a  pipe  line  could  be  cleared  up  if 
it  were  possible  to  cover  the  pipe  with  a  conducting  coating 
which  would  not  be  corroded  when  the  current  passed  from  the 
pipe  line  into  the  earth.  Most  of  the  non-corrosive  metals  are 
so  expensive  as  to  make  their  use  commercially  impracticable. 
Black  oxide,  or  coke  particles  in  a  suitable  binder,  fulfill  the 
requirement  as  regards  non-corrosive  properties,  but  the  same 
difficulties  are  here  encountered  as  in  the  use  of  paints  and  dips. 
It  is  very  difficult  to  get  a  uniform  surface  free  from  flaws.  In 
addition,  black  oxide  is  electronegative  to  iron  and  there  is 
danger  of  local  galvanic  action  being  set  up. 

Insulating  Joints. — Very  beneficial  results  have  attended  the 
practice  of  breaking  up  the  electrical  continuity  of  pipe  lines  by 
the  use  of  an  insulating  medium  at  every  joint.  If  the  installa- 
tion cost  is  too  great  to  warrant  the  insulation  of  every  joint, 
the  insulation  may  be  used  at  greater  intervals  in  the  line  pro- 


ELECTROLYSIS  287 

vided  test  readings  are  taken  to  detect  excessive  potential  drop 
between  insulated  sections.  If  the  voltage  difference  between 
two  sections  is  too  great,  there  will  be  a  shunting  of  the  current 
around  the  insulation  and  a  corrosion  of  the  pipe  on  one  side  of 
the  joint. 

Cement  is  very  commonly  used  as  the  insulating  medium; 
and  while  it  is  not  strictly  an  insulator,  if  used  at  intervals 
sufficiently  frequent,  its  resistance  will  be  high  enough  to  reduce 
the  current  carried.  Various  special  types  of  insulated  joints 
using  fiber,  wood,  leadite  or  other  substances  have  been  used  with 
apparent  success. 

The  use  of  insulating  joints  is  especially  recommended  at  the 
point  where  service  connections  are  made  to  a  building.  These 
joints  prevent  loading  up  the  pipes  inside  a  building  with  stray 
current  and  minimize  fire  hazard. 


FIG.  144. — Cable  damaged  by  electrolysis. 

Insulating  joints  are  valuable  as  an  auxiliary  means  of  reducing 
trouble  from  electrolysis  but  should  not  be  used  as  a  substitute 
for  some  of  the  more  positive  methods,  such  as  the  limitation 
of  voltage  drop  along  railway  returns. 

Protecting  Cable  Sheaths. — Thus  far  the  problem  of  electroly- 
sis has  been  considered  only  with  a  view  to  protecting  such  struc- 
tures as  gas  and  water  pipes.  Where  conditions  are  favorable  to 
electrolysis,  the  destruction  of  the  sheaths  of  lighting,  power,  and 
telephone  cables  is  much  more  rapid  and  disastrous. 

Since  the  electrochemical  equivalent  of  lead  is  about  four 
times  that  of  iron,  and  the  lead  in  the  sheath  is  just  thick  enough 
to  give  sufficient  protection  and  mechanical  support  to  the 
insulation,  it  will  be  seen  that  a  cable  will  fail  in  a  much  shorter 
time  than  a  pipe  line  carrying  the  same  current. 

Fig.  144  is  a  photograph  of  a  section  of  a  three-conductor 
transmission  cable  which  was  damaged  by  electrolysis  in  a  wet 
manhole. 


288     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

The  character  of  the  duct  construction  will  determine  to  a 
large  extent  the  amount  of  current  leaking  from  railway  systems 
to  the  cable  sheaths.  All  duct  structures  will  admit  moisture 
to  a  greater  or  less  degree,  but  fiber  duct  laid  in  concrete  admits 
less  than  other  forms  of  construction.  Where  water  does  enter, 
there  will  in  general  be  an  exchange  of  current  either  from  sheath 
to  sheath  through  the  concrete  or  between  sheaths  and  external 
structures.  It  is,  therefore,  important  that  duct  lines  be  so 
graded  as  to  drain  toward  manholes,  and  that,  as  far  as  possible, 
manholes,  be  kept  dry  by  drain  connections  to  sewers. 

The  usual  method  of  protecting  cable  sheaths  is  by  the  use 
of  a  drainage  system  similar  to  that  used  for  the  protection  of 
pipe  lines.  The  object  of  draining  the  sheaths  is  to  make  them 
slightly  lower  in  potential  than  the  surrounding  earth  or  neigh- 
boring structures,  thus  preventing  current  flowing  off  the  sheaths. 
Since  there  is  danger  of  overdraining  in  making  the  sheath  po- 
tential considerably  lower  that  that  of  ground  or  adjacent 
grounded  structures,  it  is  sometimes  necessary  to  insert  suitable 
resistances  in  the  drainage  leads.  Overdrained  cable  sheaths 
are  a  source  of  danger  to  neighboring  pipe  lines  because  of  the 
tendency  of  these  lines  to  be  injured  by  the  drainage  of  their 
current  to  the  cable  sheaths.  To  prevent  electrolysis  of  the 
sheath  of  cables  by  an  exchange  of  current  between  sheaths, 
it  is  standard  practice  to  attach  a  common  bond  in  every  manhole 
which  equalizes  the  sheath  potential  of  all  the  cables  in  the 
duct  line. 

It  is  inadvisable  to  bond  direct  to  the  track  or  railway  return, 
since  this  makes  a  cable  system  a  parallel  return  to  the  railway 
system.  Where  bonds  are  so  installed,  an  accidental  high 
resistance  in  the  railway  return  will  throw  upon  the  sheaths  the 
burden  of  carrying  a  large  part  of  the  return  current.  This 
condition  will  result  in  serious  overheating  of  the  sheaths  and, 
in  the  case  of  power  cables,  in  a  considerable  reduction  of  current- 
carrying  capacity. 

To  prevent  excessive  currents  on  cable  sheaths,  the  use  of 
insulating  joints  in  a  run  of  cable  is  sometimes  resorted  to.  This 
method  should  be  used  only  with  great  care  since  there  is  danger 
of  setting  up  excessive  potentials  across  the  joint  or  between 
the  sheath  and  ground.  As  in  the  case  of  insulated  pipe  joints, 
insulated  sheath  joints  are  used]  chiefly  to  prevent  the  entrance 
of  stray  currents  into  buildings  through  lateral  connections. 


ELECTROLYSIS  289 

The  use  of  insulated  return  feeders  provides  the  most  satis- 
factory means  of  preventing  electrolysis.  The  cost  of  this 
system  compares  favorably  with  those  now  in  use,  and  except 
in  cases  where  there  exists  a  large  investment  in  bonding  or  other 
systems,  its  use  is  recommended. 

Where  insulated  return  feeders  are  used,  the  connection 
between  the  tracks  or  other  return  conductors  and  the  station 
negative  bus  is  removed,  and  insulated  leads  are  run  out  to 
various  points  in  the  track.  By  draining  the  track  at  numerous 
points,  the  potential  gradient  along  the  rail  is  reduced  to  any 
desired  value,  and  high-current  densities  are  avoided.  It  will 
be  seen  from  Fig.  145  that  the  current  flows  from  both  directions 
into  the  return  lead,  thus  preventing  the  existence  of  a  high- 
Track 


Substation 

FIG.  145. — Reduction  of  track  gradient  by  use  of  insulated  return  feeders. 

voltage  difference  between  any  two  points  in  the  track.  It  is 
possible  to  obtain  practically  any  desired  reduction  in  potential 
gradient  along  the  track  and  to  eliminate  excessive  drop  between 
foreign  structures  and  rails  by  proper  design  of  the  return  feeders. 
It  is  true  that  by  the  use  of  this  system  some  of  the  conductivity 
of  the  track  is  sacrificed,  but  this  sacrifice  seems  justified  by  the 
excellent  results  obtained  in  practice. 

Insulated  return-feeder  systems  are  in  use  in  New  York  City, 
Springfield,  Ohio,  and  St.  Louis,  Mo.  For  a  complete  description 
of  this  system  and  of  the  methods  of  calculating,  the  number  and 
size  of  feeders,  the  reader  is  referred  to  Technologic  Paper  No.  52 
of  the  Bureau  of  Standards.  The  simple  insulated  return- 
feeder  system  will  serve  the  purpose  in  most  cases  but  where 
long  or  heavily  loaded  railway  lines  are  used,  it  is  sometimes 
necessary  to  make  use  of  either  direct  or  inverted  boosters. 

19 


290     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

Another  remedial  measure  has  been  proposed  for  the  relief 
of  electrolysis.  This  consists  in  a  periodic  reversal  of  polarity 
on  the  railway  system ;  and  while  this  method  would  theoretically 
reduce  materially  the  corrosion,  in  a  large  and  complicated  system, 
the  operating  difficulties  would  make  the  scheme  impractical 
even  if  the  reversal  were  as  infrequent  as  once  in  24  hr. 

Other  schemes  such  as  the  double-trolley  and  negative-trolley 
systems  have  been  proposed.  The  first  is  open  to  the  objec- 
tion of  excessive  cost  and  increased  operating  difficulties.  The 
second,  while  it  would  undoubtedly  delay  the  ultimate  destruc- 
tion of  other  structures,  would  impose  a  serious  hardship  on  com- 
panies which  had  installed  drainage  systems. 

General  Practice. — A  canvass  of  56  of  the  larger  lighting  companies 
operating  about  200,000  miles  of  underground  lighting  and  power  cables 
yielded  the  following  information  as  to  practice  as  regards  electrolysis 
mitigation. 

CONDUITS 

Vitrified-clay  tile,  of  both  single  and  multiple  type,  is  used  exclusively  by 
43  per  cent,  of  the  companies.  Vitrified  tile  and  indurated  fiber  is  used  by 
43  per  cent,  of  the  companies.  In  recent  years  the  use  of  vitrified  tile  has 
been  abandoned  in  favor  of  fiber  in  most  of  these  systems.  Indurated 
fiber  is  being  used  exclusively  by  12.5  per  cent,  of  the  companies.  The 
remaining  1.5  per  cent,  is  made  up  of  companies  who  either  have  not  specified 
the  type  of  conduit  used  or  else  have  in  use  a  type  which  is  not  yet  standard. 

The  tendency  to  abandon  the  use  of  sectional  tile  conduit  in  favor  of 
fiber  is  significant.  Not  only  does  fiber  conduit  afford  a  continuous  runway, 
but  its  waterproofing  and  insulating  properties  must  inevitably  serve  to 
minimize  the  danger  of  electrolytic  corrosion  at  some  point  outside  of  a 
manhole  where  the  destruction  action  might  continue  undetected  until  the 
cable  failed. 

ELECTROLYSIS 

Electrolysis  was  reported  as  existing  on  the  cable  system  by  64  per  cent, 
of  the  companies.  Evidence  that  the  trouble  is  confined  to  isolated  cases 
is  furnished  by  the  fact  that  in  only  three  instances  was  electrolysis  reported 
as  generally  existent  throughout  an  entire  system.  The  cause  of  the  elec- 
trolytic action  was  in  most  cases  attributed  to  stray  railway  currents  leaving 
the  cable  sheaths  to  select  paths  of  lower  resistance  to  the  railway  return 
systems.  Two  companies  state  that  attempts  have  been  made  to  remedy 
the  condition  by  insulating  sections  of  the  cable.  Of  these,  one  appears  to 
have  been  successful,  and  the  other  reports  that  the  trouble  still  exists  in 
spite  of  the  fact  that  each  insulated  section  is  drained  to  a  driven  ground 
connection. 


ELECTROLYSIS  291 

BONDING  OP  CABLE  SHEATHS 

The  practice  of  bonding  the  cable  sheaths  together  as  a  means  of  equaliz- 
ing sheath  potentials  and  of  preventing  electrolysis  between  sheaths  of 
adjacent  cables  is  shown  to  be  quite  general. 

Bonds  are  used  by  89  per  cent,  of  the  companies,  leaving  only  11  per  cent, 
which  use  no  bonds.  Except  in  the  case  of  three  companies,  which  employ 
lead  strip,  the  universal  practice  is  either  to  use  copper  wire  or  copper  ribbon 
sweated  directly  to  the  cable  sheaths.  In  one  instance  a  company  reports 
sweating  the  bonding  ribbon  into  one  end  of  the  cable  joint  sleeve,  a  method 
which  is  at  once  unique  and  effective. 

The  necessity  of  insulating  cable  sheaths  from  their  supporting  racks  in 
manholes  appears  to  be  doubtful. 

Of  the  replies  received,  60  per  cent,  of  the  companies  do  not  insulate. 
It  would  appear  that  the  companies  who  do  attempt  to  insulate  have  more 
trouble  from  electrolysis  where  cables  are  insulated  from  racks  than  where 
they  are  not.  This  is  probably  due  rather  to  local  conditions  than  to  the 
method  of  racking  cables. 

Of  those  using  some  form  of  rack  insulation,  23  per  cent,  use  porcelain 
saddle  blocks.  Slate,  brick,  alberene  or  concrete  shelves  are  used  by  14 
per  cent.  Wood  blocks,  old  rubber  hose  or  fiber  sections  cut  from  old  lengths 
of  conduit  are  employed  by  35  per  cent.  An  unintentional  insulation  is 
obtained  by  27  per  cent,  which  use  a  non-conducting  form  of  cable  fire- 
proofing. 

Except  in  the  case  of  those  who  use  porcelain  saddle  blocks,  the  value  of 
such  forms  of  insulation  for  establishing  conditions  adverse  to  the  action  of 
electrolysis  appears  very  doubtful. 

Probably  the  only  real  value  of  any  of  these  materials  is  to  furnish  a  form 
of  mechanical  support  which  protects  the  lead  sheaths  against  the  rough 
edges  of  the  manhole  racks.  A  more  effective  protection  would  be  obtained 
by  the  use  of  a  piece  of  sheet  lead  cut  from  the  cable  strippings. 

The  practice  of  draining  a  cable  system  to  the  street  railway  return 
system  at  the  negative  bus  in  substations,  or  to  negative  conductor  or  tracks 
at  points  close  to  substations  is  rapidly  becoming  standard. 

That  the  drainage  system  affords  real  protection  to  cable  sheaths  is  proved 
by  the  fact  that  66  per  cent,  use  this  system  and  have  noted  that  electrolysis 
under  this  method  of  bonding  is  negligible. 

Many  companies  connect  also  to  other  grounded  systems.  Connections 
to  gas  or  water  pipes  are  made  by  25  per  cent,  of  the  companies,  to  system 
neutrals  by  16  per  cent.,  and  to  cable  sheaths  of  other  systems  by  7  per  cent. 
Bonding  direct  to  street-railway  tracks  is  practised  by  18  per  cent. 

The  fear  that  such  apparently  indiscriminate  connections  to  other 
systems  would  result  in  loading  up  the  cable  sheaths  with  return  currents 
from  other  systems  has  been  dispelled  by  the  results  obtained  by  companies 
using  the  drainage  system. 

It  would  appear  that  the  troubles  from  electrolysis  are  in  inverse  propor- 
tion to  the  number  of  drainage  connections  employed.  This  is  borne  out 
by  the  experience  of  two  companies  which  report  that  severe  electrolytic 
conditions  have  almost  entirely  disappeared  from  their  systems  as  a  result 


292     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

of  the  free  use  of  drainage  bonds.  This  improvement  in  conditions  has 
not  been  obtained  at  the  expense  of  the  adjacent  systems  since  tests  show  a 
marked  decrease  in  electrolytic  action  on  neighboring  structures  tied  into  the 
drainage  network. 

A  large  company  operating  in  a  city  of  about  500,000  population,  and 
which  reports  no  drainage  taps  of  any  kind,  appears  to  be  suffering  severe 
damage  by  electrolytic  corrosion.  On  the  other  hand,  a  company  which 
bonds  both  to  its  own  grounded  neutral  conductors  and  to  street  railway 
negative  return  cables  notes  absolutely  no  electrolysis  in  spite  of  the  fact 
that  much  of  its  system  is  permanently  submerged  in  salt  water. 

In  several  cases  the  drainage  connections  used  consist  of  a  network  of 
conductors  paralleling  the  cable  system.  One  report  states  that  a  network 
of  this  kind  was  installed  by  the  railway  company  for  the  purpose  of  pro- 
tecting adjacent  cables  and  structures. 

There  appears  to  be  no  ground  for  the  belief  that  sheath  currents  may 
reach  such  a  value  as  to  result  in  serious  overheating.  Forty-two  companies 
making  up  75  per  cent,  of  the  systems  reporting  state  that  they  allow  their 
cable  sheaths  to  carry  return  currents.  Of  these,  four  limit  the  currents  by 
the  use  of  resistance  inserted  in  the  drainage  leads;  four  make  periodic  in- 
spection and  test,  limiting  the  current  when  necessary  by  the  installation  of 
additional  drainage  bonds.  The  rest  make  no  attempt  to  limit  the  current. 
It  is  worthy  of  note  that  not  a  single  case  of  damage  to  a  cable  or  a  limiting 
of  capacity  due  to  overheating  has  been  reported. 

UNINSULATED  NEUTRAL 

An  uninsulated  neutral  or  return  conductor  is  used  on  either  their  high- 
or  low-tension  distribution  systems,  or  both,  by  54  per  cent,  of  the  companies 
reporting.  Of  the  companies  using  this  system,  53  per  cent,  use  their  cable 
sheaths  either  wholly  or  in  part  for  carry  ing  these  neutral  currents.  Where 
this  practice  is  followed,  it  appears  that  in  most  cases  the  neutral  wire  itself 
is  used  chiefly  as  a  common  bond  to  which  all  cable  sheaths  are  connected. 
The  return  currents  divide  inversely  as  the  resistance  of  the  paths,  and, 
except  in  cases  where  there  are  few  cables  in  a  duct  line,  the  cable  sheaths 
carry  the  major  portion  of  the  neutral  return  currents. 

One  company  reports  the  use  of  the  cable  sheaths  as  a  neutral  for  a  trans- 
mission system,  and  several  use  their  sheaths  as  the  neutral  of  their  2,300- 
volt  or  4,000-volt  distribution  feeders. 

Only  five  cases  of  trouble  are  reported  as  resulting  from  the  use  of  cable 
sheaths  as  neutral  return  conductors.  In  one  instance  bond  wires  were 
burned  off  and  cable  sheaths  damaged  due  to  the  use  of  bonds  of  insufficient 
size.  The  trouble  was  cleared  up  by  the  installation  of  bonds  of  larger 
cross-section.  The  second  case  was  the  destruction  of  a  neutral  by  elec- 
trolytic action.  This  neutral  was  a  service  connection  tapped  off  from  an  old 
Edison  iron-tube  system  and  carried  through  a  wooden  plug  into  a  joint-box. 
A  bond  between  the  neutral  and  the  iron  tube  caused  a  disappearance  of  the 
dangerous  condition. 

The  remaining  three  cases  of  trouble  consisted  of  a  distortion  of  neutral 
potentials  on  Edison  three-wire  direct-current  networks  by  earth-potential 


ELECTROLYSIS  293 

gradients  caused  by  street-railway  return  currents.  In  two  instances  the 
difficulty  was  overcome  by  installing  additional  feeder  copper,  but  in  the 
third  case  it  was  found  necessary  to  run  insulated  neutral  wires  from  the  load 
center  affected  back  to  the  substation. 


COOPERATION  OP  UTILITIES 

Cooperation  with  the  railway  companies  is  reported  by  36  per  cent,  of  the 
companies;  with  the  telephone  companies  by  28  per  cent.;  and  with  water 
companies  or  municipalities  by  25  per  cent.  Only  11  per  cent,  report  any 
cooperation  on  the  part  of  the  gas  interests.  It  should  be  noted  that  in 
many  cases  the  reporting  companies  are  connected  either  directly  or 
indirectly  with  the  railway  systems. 

Since  there  is  no  reported  instance  of  failure  to  cure  electrolytic  action 
where  proper  cooperation  existed  between  utilities,  it  seems  clear  that  there 
should  be  little  difficulty  in  correcting  conditions  favorable  to  electrolytic 
corrosion.  The  advantages  of  the  standard  methods  in  use  have  been 
proved  conclusively,  and  there  is  no  reason  to  believe  that  the  protection 
gained  by  their  use  could  not  be  extended  to  the  underground  structures  of 
other  utilities  provided  these  utilities  were  willing  to  take  up  the  problem 
in  a  real  spirit  of  cooperation. 

Electrolysis  Surveys. — Where  trouble  from  electrolytic  cor- 
rosion is  suspected,  accurate  data  as  to  the  intensity  and  extent 
of  the  trouble  may  be  obtained  from  an  electrolysis  survey. 
Such  a  survey  is  made  by  reading,  at  intervals  along  the  streets 
on  which  railways  are  located,  the  potential  difference  between 
one  structure  and  all  the  others.  Where  an  electric  central-sta- 
tion company  is  making  the  survey  it  is  usual  to  assume  the 
cable  sheaths  as  the  datum  or  potential  zero.  The  potential 
difference  between  the  cables  in  each  manhole  and  neighboring 
tracks,  water  pipes  or  gas  pipes  is  read  by  means  of  a  high- 
resistance  voltmeter.  A  meter  well-adapted  for  electrolytic  work 
is  the  Weston  duplex  instrument  illustrated  in  Fig.  146. 

For  the  potential  readings,  contact  is  secured  by  means  of  rods 
for  the  cable  sheaths  and  a  screw-driver  point  for  other  structures 
or  the  earth. 

The  rods  are  approximately  6  ft.  long  and  are  usually  in  two 
parts  so  that  they  can  be  easily  carried  about.  Heavy  reinforced 
lamp  cord  is  used  for  the  leads  from  the  rods  to  the  instrument. 
In  Fig.  147  rods  are  shown  which  have  been  used  to  advantage 
by  the  testing  department  of  the  Brooklyn  Edison  Co.  In  taking 
current  readings,  flexible  rubber-covered  wire  of  the  proper  re- 
sistance is  used  to  give  the  correct  millivolt  reading.  The  bare 


294     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

ends  of  these  leads  are  held  on  the  cable  sheaths  by  one  man  while 
another  reads  the  meter. 

The  field  notes  should  be  copied  on  cards  similar  to  that  shown 
in  Fig.  148  and  made  a  part  of  a  special  electrolysis  file.  These 
cards,  in  addition  to  the  voltage  readings,  have  space  for  a  gen- 
eral description  of  the  conditions  existing  at  the  time  of  the  test. 
After  the  collection  of  the  field  data  a  skeleton  map  of  the  city  or 
district  affected  is  used  to  give  a  graphic  presentation  of  the  ex- 


FIG.  146. — Weston  duplex  electrolysis  instrument. 

isting  conditions.  The  railway  lines,  duct  lines,  water  pipes,  and 
other  structures  are  drawn  in  their  proper  location  and  the  poten- 
tial difference  between  the  cable  sheaths  and  other  structures  are 
platted  normal  to  the  direction  of  these  structures.  Positive 
voltages  are  laid  off  in  one  direction  and  negative  voltages  in  the 
other. 

Since  the  Weston  test  meter  is  a  duplex  instrument,  it  is  possi- 
ble also  to  measure  the  current  carried  on  the  cable  sheaths  by 
obtaining  the  millivolt  drop  over  a  given  length.  The  amperes 


ELECTROLYSIS 


295 


per  millivolt  is  a  constant  for  a  given  cable,  and  by  using  the 
constant  as  a  multiplier,  the  value  of  sheath  current  is  obtained. 
By  measuring  the  current  carried  on  the  cables  in  every  man- 
hole, it  is  possible  to  learn  the  approximate  location  of  the  point 


I         Q 


NOTE: 


X  Steel  Dowel  Pin 


Attach  15  ft. piece  of  reinforced  lamp  cord 
soldering  an  end  on  snrface  of  coupling  anc 
taping  entire  rod  with  friction  tape. 


NOTE: 

Attach  85  ft.  piece  of  reinforced  lamp  cord 
soldering  an  end  on  surface  of  coupling  and 
taping  entire  rod  with  friction  tape. 

Brass  Coupling 


Steel  Dowel  Pin 


Mach.  Steel  Tempered 


—  30-- 


Iron  Rod' 


30-, 


Ji"lron  Rod  v 


FIG.  147. — Electrolysis  testing  rods. 

where  the  current  is  leaving.  Where  a  marked  discrepancy  exists 
in  the  sheath  currents  in  adjacent  manholes,  an  investigation 
should  be  made  with  a  view  to  installing  metallic  drains  to  pre- 
vent the  current  leaving  through  the  ground. 


PUBLIC  SERVICE  ELECTRIC  CO. 
ELECTROtYTIC  TEST 


FIG.  148. — Electrolysis  record  card. 

The  value  of  the  electrolysis  survey  is  to  show  the  danger 
points  in  a  cable  system  and  to  indicate  the  places  where  drain- 
age bonds  should  be  installed. 


CHAPTER  X 
OPERATION  AND  MAINTENANCE 

Records. — One  of  the  essential  things  in  connection  with 
the  operation  of  an  underground  system  is  the  keeping  of  de- 
tailed permanent  records.  It  should  be  the  duty  of  every  cable 
and  underground  engineer  to  keep  a  system  of  records  which  will 
enable  him  to  tell  at  any  time  the  exact  amount  and  the  location 
of  the  cable  installed. 

Suitable  forms  should  be  provided  to  make  it  an  easy  matter  for 
the  foreman  on  the  work  to  make  the  necessary  notes,  and  these 
foremen's  reports  should  be  carefully  transferred  to  the  perma- 
nent office  records.  A  good  system  of  records  will  be  found  of 
great  value  in  locating  and  taking  care  of  trouble  and  in  laying  out 
new  work.  Such  records  will  also  be  of  assistance  to  the  commer- 
cial department  in  considering  new  business.  It  frequently  hap- 
pens, where  complete  records  are  not  kept,  that  the  company 
depends  to  a  large  extent  upon  the  memory  of  certain  employees, 
and  if  these  employees  leave  the  company  the  information  is  lost. 

Diagrammatic  layouts  of  the  conduit  system  and  manhole 
system  are  most  conveniently  kept  in  loose-leaf  or  card  form. 
These  records  are  not  drawn  to  scale,  but  show  a  diagram  of  the 
street  with  a  line  to  represent  the  conduit,  while  manholes  are 
indicated  in  their  proper  location  by  rectangles  or  other  figures 
corresponding  to  the  shape  of  the  manhole.  Measurements  are 
indicated,  showing  distances  between  centers  of  covers  and  also 
their  location  with  respect  to  curb  lines.  The  latter  is  quite 
important,  particularly  in  locations  where,  during  the  winter 
months,  snow  covers  the  ground.  Knowing  the  exact  location 
of  the  center  of  a  cover  will  save  considerable  time  for  the  cable 
men  when  inspecting  manholes  on  locating  trouble.  In  Fig.  149 
is  illustrated  a  system  of  conduit  record,  while  a  manhole  record 
card  is  shown  in  Fig.  150.  The  number  of  records  necessary  will 
depend  on  the  size  of  the  company  and  the  nature  of  the  work. 
For  a  comparatively  small  expense,  however,  records  will  be  made 
which  will  always  be  accessible. 

296 


OPERATION  AND  MAINTENANCE 


297 


Identification  of  Cables.  —  All  cables  should  be  properly 
tagged  in  every  manhole,  these  tags  to  indicate  the  size, 
voltage,  and  cable  number.  With  a  view  to  ascertaining  the 
general  practice  and  experience  of  the  larger  companies  in  regard 


PUBLIC  SERVICE  ELECTRIC  COMPANY 

CABLE    RECORD 


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FIG.  149. — Conduit  and  cable  record  card. 


to  cable  tagging  and  numbering  scheme,  the  Underground  Com- 
mittee of  the  National  Electric  Light  Association  sent  out  to 
member  companies  a  series  of  questions  relating  to  cable  tagging. 
The  replies  received  indicated  a  great  diversity  of  opinion  and 
practice.  With  the  exception  of  a  few  of  the  companies,  who 


298     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 


embody  some  very  good  features  in  their  methods  of  tagging  and 
numbering,  it  appears  that  the  matter  has  received  very  little 
attention. 

Tags  have  been  made  of  various  metals,  including  brass,  lead, 
zinc,  aluminum,  copper  and  galvanized  iron ;  brass  being  the  most 
common  in  use.  Usually  symbols  or  figures  are  stamped  into  the 
metal.  A  good  form  of  tag  is  one  in  which  the  figures  are  cut 

PUBLIC  SERVICE  ELECTRIC  COMPANY 

MANHOLE.  INSPECTION  CARD 
MANHOLE  H0+O/-S.£.Corner  ^Qctcr\o^^aing  First  Strs.    C)TY  Mewar-k,N.*J. 

BUILT     /V7>1>»-/?/*  KINO    CO/MC*ET.£.  SIZE   6  ^  X  B  ^T  And  £  &.  pe &JO, 


-Z— 

HAIL 

OAS 

NECESSARY   REPAIRS  OR  CHANGES 

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TRANSFORMER  AND  BOX   RECORD 


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S-fol* 

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O.K. 

FIG.  150. — Manhole  record  card. 

through  the  middle  in  the  form  of  a  stencil.  With  the  figures  or 
symbols  punched  through  the  metal,  the  legibility  should  not  be 
affected  by  any  ordinary  corrosion.  The  punching  should  form 
plain  open  figures  without  any  frail  bars  of  metal  left  to  cause 
confusion.  A  tag  as  just  described  is  shown  in  Fig.  151,  the 
shape  of  the  tag  illustrated  indicating  the  class  of  service  for  which 
the  cable  is  used. 

A  tag  made  of  sheet  lead,  similar  to  the  lead  sheath  of  the 


OPERATION  AND  MAINTENANCE 


299 


Hole  for  Fastening 


cable  and  subject  to  the  same  exposure,  would  not  be  seriously 

affected  by  corrosion,  and  when  made  in  the  form  of  a  strap, 

as  shown  in  Fig.  152  can  be  passed  around 

the  cable  like  a  collar.     Glass  tags  made  to 

receive  a   card  bearing  the   cable  number 

have  been  used  by  some  companies,  but  as 

far  as  is  known  to  the  writer  have  nowhere 

been     in     service     long    enough    to    have 

thoroughly  demonstrated  their  usefulness. 

Tags  were  formerly  fastened  to  the  cables 
with  copper  wire  in  pendant  fashion ;  but  due 
to  corrosion,  tags  frequently  became  de- 
tached from  the  cable.  For  this  reason  a 
tinned  copper  bonding  ribbon  is  now  used 
for  fastening  the  tags  to  the  cable.  As  shown  in  Fig.  153,  two 
holes  are  punched  in  the  tag  to  allow  an  additional  wire  to  be 


FIG.  151.— Round- 
cable  tag. 


e  for  Fastening 


(A)    DEPENDS  ON  DIAMETER  OF  CABLE 


FIG.  152.  —  Lead-cable  tag. 

used  in  supporting  the  tag,  thus  insuring  its  proper  fastening 
to  the  cable.     Tags  should  be  fastened  to  the  cables  at  or  close 

to  the  joint.     This  makes  them 

^^    ^   find   ^    congegted    man_ 

holes. 

There  are  various  numbering 
schemes  in  use  for  designating 
cables  and  in  some  cases  attempts 
have  been  made  to  indicate,  in 
addition  to  the  serial  number  of 
the  cable  itself,  the  voltage,  class 
of  service,  source  and  destination. 

FIG.  153.—  High-tension-cable  tag.  TaSs  of  different  shapes  have  been 

used  to  advantage  and  some  com- 
panies have  adopted  sharp-pointed  tags,  Fig.  153,  for  marking 


300     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

high-tension  feeders.  By  choosing  different  ranges  of  numbers 
for  different  classes  of  distribution,  distinction  can  be  made  as 
to  the  class  of  service.  Letters  of  the  alphabet  are  sometimes 
combined  with  numerals  to  show  class  distinction.  The  follow- 
ing method  of  numbering  is  submitted  as  a  simple  and  ready 
means  of  identification. 

Secondary  mains,  110-volt numbers     100  to     199  inclusive. 

Secondary  mains,  220-volt numbers     200  to     299  inclusive. 

Primary  feeder,  single-phase,  2, 400-volt.  numbers  2,400  to  2,499  inclusive. 

Primary  feeder,  two-phase numbers  4,800  to  4,899  inclusive. 

Series-arc  circuits numbers  7,500  to  7,599  inclusive. 

From  the  foregoing  it  is  noted  that  a  number  may  be  used 
which  readily  indicates  the  voltage  of  the  circuit.  While  num- 
bering schemes  are  good,  it  must  be  remembered  that,  as  a  rule 
a  given  method  is  applicable  only  to  its  particular  cable  system. 
The  design  and  development  of  any  scheme  is  influenced  by  so 
many  local  factors  that  each  must  be  worked  out  independently 
to  suit  the  requirements.  Whether  the  numbers  are  placed  on 
tags  or  in  record  books,  they  must  be  simple,  capable  of  expansion 
without  complications,  and  they  should  preferably  be  indicative 
to  some  degree  of  some  function  the  cable  performs. 

The  use  of  loose-leaf  cable-record  books  in  which  duct  loca- 
tions are  given  and  which  can  be  used  as  a  reference  in  the  field 
to  check  the  cable  tagging  is  very  desirable.  This  form  of  record 
has  proved  highly  satisfactory  for  both  field  and  office  use. 

In  addition  to  proper  tagging  some  additional  safeguard  is 
usually  desirable  in  order  to  remove  every  possibility  of  workmen 
cutting  into  a  live  cable.  An  exploring  coil  has  been  used  to 
advantage  in  the  field  to  pick  up  a  signal  on  the  desired  cable 
which  has  a  special  signal  current  impressed  upon  its  conductor 
terminals.  This  same  exploring  coil  and  interrupter  is  also  used 
in  many  cases  in  the  field  to  phase  out  the  conductors  of  a  multi- 
ple-conductor cable.  Spiking  is  often  resorted  to  as  a  last  precau- 
tion before  cutting  into  a  supposedly  dead  cable,  but  is  not  recom- 
mended as  good  practice,  because  of  its  unreliability  as  it  is  done 
by  some  cablemen. 

In  Chapter  VI,  under  the  heading  "Testing  for  Live  Cable," 
several  methods  which  are  considered  good  practice  are  described. 

Record  of  Cable  and  Equipment  Failures. — A  system  of 
recording  cable  failures  and  subway  troubles  is  of  considerable 
value.  Interruption  to  service  caused  by  the  failure  of  a  cable 


OPERATION  AND  MAINTENANCE  301 

or  other  equipment  should  be  thoroughly  investigated  by  the 
foreman  or  cableman  in  charge,  and  a  complete  report  giving 
full  details  should  be  kept  on  file  for  future  reference.  If  the 
troubles  are  numerous  a  detailed  record  will  greatly  assist  in 
determining  what  changes  are  necessary  to  improve  the  system. 

PUBLIC  SERVICE   ELECTRIC  COMPANY 


REPORT  OF  HIGH  TENSION  FEEDER  TROUBLE 

.Date  ---------------  .Time  _____________  Feeder  No  ________  .  ___  from  _____________ 

To  --------------  Size  -------------  Operating  voltage  ____________  Frequency  ______ 

Insulating  material  ------------------  Insulation  thickness  __________  Condition  _____ 

Made  by  --------------------------  Installed,  date  ______________  by  ___________ 

Length  of  underground  portion  ________________  ft.        overhead  ___________________    ___  ft. 

First  indication  of  trouble  __________________________ 

Nature  of.  trouble  ___________________________  Eeported  by  ______________________ 

Trouble  occnrred  during  test.  ___________________  or  feeder  in  service  ________________ 

Previous  to  breakdown,  load  on  feeder.  _____________________  Max.  air  temperature  ________ 

LOCATION  OF  FAULT 
Fault  located  by;  Fault  located  in: 

Inspection  -------------------------         Manhole    in  joint  _____________________ 

Report  of  _________________________  ,  in  bend  __________________ 

in  straight 
loop  test  -------------------------  length  ____________________ 

Fault  detector.  _____________________  Duct  _  ft.  from  duct  edge. 

Cut  and  try.  ------  No.  of  cuts  __________  '        Eepairs  completed  at  __________________ 

Time  required  to  locate  ----------------  Feeder  ready  for  service  at 

Section  of  conduit  ------------------  '..  Location  of  duct  occupied  _______________ 

PROBABLE  CAUSE  OF  TROUBLE 

(a)  Mechanical  injury: 

1.  Extraneous  mechanical  ________________________________ 

2.  'Electrolysis  ________________________________________ 

3.  Sharp  bend  __________________________ 

.4.        Overheating  _____________________________________ 

(5         Surge  on  system)  _____ 

(6)  .Defect  in  cable: 

1.  Defective  insulation  ________________________________ 

2.  Defective  sheath  _______________________________  J 

3.  Defective  joint  _________________  Made  by  _____________ 

(c)    Cau.se  unkno.wn_____  __ 


^Resulting  damage  in  conduit  or  manhole 

"  "         "  station  or  substation 

Detail  report  of  trouble  of on  cable  No. 

On  reverse  side  give  detailed  report 

FIG.  154.— Cable-trouble  sheet. 

In  order  to  secure  comparative  information  it  is  desirable  that 
reports  be  made  up  on  a  standard  form  such  as  that  submitted 
herewith,  Fig.  154,  for  reporting  high-tension  feeder  trouble. 
This  form  which  has  been  drawn  up  to  cover  all  ordinary  cases 
of  trouble,  may  be  made  up  in  card  form  for  convenience  in  filing. 


302     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

If  this  is  done,  some  reduction  may  be  made  in  the  size  of  the 
report.  It  is  very  desirable,  however,  that  in  entering  the  in- 
formation under  the  headings  ' 'Location  of  Fault"  and  " Probable 
Cause  of  Injury"  the  foreman  should  have  the  accompanying 
form  of  report  at  hand  and  make  entries  on  the  form  under 
one  of  the  several  subheadings.  The  back  of  the  report  should 
be  used  for  describing  previous  troubles  on  the  same  line  or  in 
the  same  conduit,  which  may  possibly  have  had  a  bearing  upon 
the  fault,  as  well  as  other  items  of  interest  which  cannot  be 
readily  tabulated. 

Cleaning  Manholes. — Underground  systems  require  much  less 
attention  than  overhead  lines,  but  it  is  a  mistake  to  suppose  that 
when  lines  are  once  underground  they  will  care  for  themselves. 
There  is  always  a  chance  for  trouble.  Provision  should  be  made 
for  cleaning  manholes  at  regular  intervals,  these  cleanings  being 
sufficiently  frequent  to  prevent  insanitary  conditions  in  manholes. 
A  number  of  companies  maintain  portable  pumping  equipments 
which  are  used  by  a  regular  inspection  and  cleaning  division 
employed  solely  in  maintaining  the  underground  system  in  a 
satisfactory  condition.  Before  beginning  work  in  manholes 
where  obnoxious  odors  or  other  disagreeable  conditions  exist, 
an  effort  should  be  made  to  supply  forced  ventilation  or  adopt 
other  expedients  which  will  make  the  conditions  in  the  manhole 
tolerable  for  the  workmen.  Increasing  interest  in  the  welfare 
of  employees  is  daily  becoming  more  evident  both  on  the  part 
of  the  operating  companies  and  the  public  authorities  having  to 
deal  with  such  matters.  In  a  large  system  a  considerable  saving 
in  the  cleaning  of  manholes  can  be  affected  by  a  systematic  pro- 
cedure in  the  use  of  large  dump  wagons  and  a  small  gang  of  men, 
who,  when  work  on  the  cleaning  of  manholes  is  slack,  join  the 
various  conduit  and  cable  gangs. 

Care  of  Cables. — If  a  large  number  of  loaded  cables  pass 
through  one  manhole  it  is  well  to  take  temperature  readings 
in  the  manhole  to  determine  when  a  temperature  unsafe  for 
the  cable  is  reached;  these  can  be  taken  either  with  a  recording 
thermometer  or  one  giving  maximum  temperature.  In  cold 
weather,  or  when  the  streets  are  muddy,  it  is  sometimes  advisable 
to  have  an  inspector  go  over  heavily  loaded  conduit  lines  to 
make  sure  that  the  ventilating  holes  in  the  manholes  covers 
are  open. 

In  Fig.  155  are  shown  curves  of  manhole  temperature,  tern- 


OPERATION  AND  MAINTENANCE 


303 


perature  of  outside  air  and  load  on  the  cables  passing  through 
a  manhole.  The  hole,  which  is  7  by  7  ft.,  and  7  ft.  deep,  contains 
two  50~kw.  transformers.  It  will  be  noted  from  the  size  of  the 
manhole  that  there  are  3.43  cu.  ft.  of  space  per  kw.  of  trans- 
former capacity.  This  is  considered  conservative  and  in  this 
particular  case  did  not  result  in  excessive  manhole  temperatures. 
Periodic  insulation  resistance  tests  are  valuable,  as  they  furnish 
indications  of  abnormal  conditions  and  often  lead  to  the  detection 
of  faults  on  the  system.  A  new  cable  should  not  be  connected 
to  the  main  busbars  without  being  previously  tested  with  full 
working  pressure.  This  is  usually  accomplished  through  a  suit- 


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TOTAL  SQUARE  FEET  INCLUDING  TOP 
AND  BOTTOM  294 
Transformer  60  Kw.  Core  Loss     297 
Copper  Loss  596 
Total          893 
Losses  for  Two  Transformers                       178C  Watts 
Watts  Loss  Square  Foot                               6.08 
8.48  Cu.  Ft.  per  Kw.  of  Transformers  Capacity 

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FIG.  155.— Manhole-temperature  chart  showing  comparison  of  temperature 
with  load  on  cables. 

able  transformer  properly  fused,  or  by  inverting  a  rotary  conver- 
ter with  a  fuse  on  the  low-tension  side. 

The  feeder  readings,  taken  in  stations  and  substations,  should 
be  carefully  followed  up  to  make  sure  that  no  feeders  are  over- 
loaded and  the  load  on  the  mains  should  also  be  noted.  For 
the  purpose  of  checking  the  load  on  single-conductor  cables, 
particularly  transformer  leads,  a  split-core  current-testing 
transformer  will  be  found  convenient.  This  instrument,  which 
is  illustrated  in  Fig.  156,  consists  of  a  special  transformer  having 
a  hinged  magnetic  circuit  and  a  standard  portable  ammeter. 
Flexible  duplex  leads  are  supplied  with  each  set,  of  sufficient 
length  so  that  the  transformer  can  be  clamped  in  position  around 
the  conductor  and  the  ammeter  removed  to  a  more  convenient 


304     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

place  for  reading.  When  a  test  is  to  be  conducted,  the  terminals 
of  the  duplex  leads  should  be  inserted  in  the  ammeter  binding 
posts  and  the  transformer  jaws  firmly  clamped  in  position  around 
the  cable.  The  transformer  will  maintain  within  commercial 
limits  its  ratio  accuracy  from  one-eighth  to  25  per  cent,  overload. 
Occasions  constantly  arise  for  using  this  set  in  determining 
the  load  on  feeders  and  in  the  case  of  distribution  networks, 
where  it  has  been  found  particularly  valuable. 


FIG.  156. — Split-core  cable-testing  transformer. 

A  regular  inspection  of  the  manholes,  covers,  cables,  junction 
boxes  and  other  equipment  should  be  made  from  two  to  four 
times  a  year  depending  on  the  size  of  the  system,  and  a  record 
kept  of  such  inspection,  together  with  all  necessary  work  done 
to  maintain  the  entire  system  at  maximum  efficiency. 

Cables  should  not  be  disturbed  after  once  in  place,  if  it  is  possi- 
ble to  avoid  it.  If  they  must  be  moved,  it  should  be  done  with 
the  greatest  care,  one  cable  at  a  time  and  without  any  strain 
on  the  cable  joints. 


OPERATION  AND  MAINTENANCE  305 

Cables  should  never  be  used  as  steps  for  entering  or  leaving 
manholes.  A  small  portable  ladder  should  always  be  used  for 
this  purpose. 

It  is  not  possible  to  estimate  accurately  the  life  of  cables  and 
what  will  be  the  cost  of  maintenance  after  several  years'  installa- 
tion. The  cost  of  repairs  for  the  first  year  is  usually  very  low 
and  the  other  items  of  maintenance  are  the  expenses  for  periodic 
inspection  and  testing. 

Bonding  Cables  in  Manholes. — The  following  recommenda- 
tions are  made  by  the  Underground  Committee  of  the  National 
Electric  Light  Association  in  the  matter  of  the  bonding  of  all 
cables  in  each  manhole. 

It  is  of  prime  importance  when  faults  occur  in  underground 
cables;  that  the  current  flowing  in  the  short-circuit  should  be 
sufficient  to  operate  the  safety  devices  or  in  the  absence  of  safety 
devices  to  make  a  sufficient  disturbance  so  that  the  existence  of 
the  trouble  will  be  quickly  brought  to  the  attention  of  the  station 
operator.  In  the  case  of  single-conductor  cables,  whether  for 
use  on  Edison  three- wire  systems  having  a  normal  voltage  of  115 
or  230,  or  on  railway  systems  having  a  normal  voltage  of  about  600, 
it  is  entirely  possible  that  a  short-circuit  may  occur  between  the 
conductor  and  the  lead  at  a  point  remote  from  the  power  supply 
station  without  a  sufficient  rise  in  the  current  to  enable  the  opera- 
tor to  distinguish  it  from  some  unusual  load.  The  lead  sheaths 
of  1,000,000-  and  1,500,000-cm.  cables,  which  are  the  sizes  fre- 
quently used,  are  equivalent  to  about  70,000  and  80,000  cm.  in 
copper,  respectively,  so  that  if  the  current  which  passes  through 
the  short-circuit  from  the  conductor  to  the  lead  is  required  to  tra- 
verse only  a  few  blocks  of  the  lead  of  that  particular  cable  before 
it  can  find  other  paths  to  the  station,  the  resistance  may  be  suffi- 
cient to  limit  the  current  to  the  normal  carrying  capacity  of  the 
copper.  The  radiating  surface  of  the  lead  is  so  great  that  this 
large  amount  of  current  may  be  carried  for  quite  an  appreciable 
time  without  seriously  overheating  the  lead.  The  result  is  that 
the  arc  at  the  point  where  the  trouble  started  has  in  series  with  it 
sufficient  resistance  so  that  it  burns  quite  steadily  and  without 
the  knowledge  of  the  station  operator.  This  is  probably  the  most 
dangerous  trouble  that  can  occur  on  an  underground  system  and 
every  effort  should  be  made  to  avoid  the  occurrence  of  such  a 
condition. 

The  use  of  concentric  cable  eliminates  the  above-mentioned 
20 


306     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

difficulty,  as  an  arc  of  this  kind,  even  if  it  starts  in  the  outer  con- 
ductor, is  very  quickly  communicated  to  the  inner,  and  enough 
current  will  flow  in  the  short-circuit  to  eliminate  any  doubt  on  the 
part  of  the  operator  as  to  the  nature  of  the  trouble.  Where 
single-conductor  cables  are  already  installed,  the  condition  can 
generally  be  improved  by  bonding  the  lead  sheaths  of  all  cables 
in  each  manhole.  This  will,  in  general  give  sufficient  conductiv- 
ity in  the  return  path  to  cause  enough  current  to  flow  at  the  point 
of  the  trouble  so  that  the  existence  of  the  trouble  is  immediately 
apparent.  The  calculations  to  determine  the  possible  amount 
of  current  that  will  flow  are,  however,  very  simple  and  should 
always  be  made  as  a  check  whenever  there  is  any  doubt  on  this 
point. 

The  bonding  of  the  cables  in  all  manholes  also  reduces  the 
liability  of  damage  due  to  electrolytic  action  by  stray  currents  of 
electric  railways,  as  well  as  similar  damage  due  to  leaky  joints 
and  other  troubles  on  the  lighting  cables.  While  there  is  some 
difference  of  opinion  among  experts  on  the  subject  as  to  the  ex- 
act scheme  of  protection  that  should  be  adopted  for  lead-covered 
cables  operated  by  a  lighting  company,  they  are  in  accord  on  the 
proposition  that  the  lead  sheaths  of  all  cables  be  bonded  together 
in  all  manholes. 

When  bonding  cables  the  important  feature,  necessary  for  good 
results,  are  a  positive  low-resistance  connection  to  the  lead 
sheath  and  a  conducting  medium  from  one  cable  sheath  to  the 
other.  Experience  has  proved  that  either  copper  ribbon  or 
copper-tinned  wire  give  the  best  results.  A  choice  between  the 
two  is  simply  a  matter  of  opinion  and  minor  manhole  require- 
ments, the  wire  having  the  advantage  of  a  more  flexible  bond  than 
the  ribbon,  when  such  is  an  advantage. 

Rules  and  Requirements. — In  large  systems  it  is  impor- 
tant to  devise  a  set  of  rules  for  the  guidance  of  the  men  in  the 
different  departments.  These  rules  must  be  rigidly  complied 
with  so  as  to  eliminate  any  danger  of  injury  to  men  making 
tests  or  repairs  to  cable  or  switchboards.  While  it  is  impossible 
to  include  in  a  brief  summary  complete  instructions  covering 
every  detail  in  connection  with  underground  work,  the  follow- 
ing rules  are  intended  to  lay  down  certain  fundamental  princi- 
ples, which  should  be  observed  in  all  cases.  To  avoid  accidents 
to  employees  or  the  public,  the  following  rules  and  cautions  are 
recommended. 


OPERATION  AND  MAINTENANCE  307 

SUBWAY  RULES 

Every  splicer,  inspector,  and  helper,  must  observe  the  follow- 
ing: 

LOOK  OUT  FOR  GAS 

Immediately  upon  opening  a  manhole  or  vault  and  before  en- 
tering same,  make  a  careful  examination  for  illuminating,  sewer, 
or  other  harmful  gas.  Never  enter  a  manhole  where  poisonous 
gas  is  found,  but  report  same  promptly  to  foreman  or  superintend- 
ent in  charge. 

If  it  is  necessary  to  work  in  a  manhole  which  does  not  venti- 
late properly  after  the  cover  has  been  removed,  an  air  pump  must 
be  used.  A  rope  must  be  attached  to  the  body  of  the  workman 
in  the  manhole  and  fastened  above,  so  that  in  case  of  necessity, 
he  can  be  drawn  to  the  surface.  Work  of  this  character  must  be 
done  only  when  expressly  ordered  by  the  foreman  or  superinten- 
dent and  under  his  direct  supervision. 

AVOID  EXPLOSIONS 

Do  not  use  matches,  lamps  or  candles  in  or  near  manholes.  If 
artificial  illumination  is  required  use  only  incandescent  lamps  or 
approved  safety  lanterns. 

Never  carry  a  gasolene  or  other  furnace  or  torch  into  or  near 
a  manhole. 

Do  not  smoke  or  carry  lighted  cigars,  cigarettes  or  pipes  into 
or  near  a  manhole. 

Avoid  sparks  in  connecting  or  disconnecting  cables  or  apparatus 
in  manholes. 

Exercise  care  in  soldering  and  wiping  joints  so  as  not  to  ignite 
the  flux. 

WATCHING  AND  GUARDING 

After  removing  a  cover  from  a  manhole,  place  around  the  open- 
ing the  guard  provided,  to  which  should  be  attached  a  red  flag. 
When  working  at  night,  substitute  a  red  light.  Always  have  a 
man  at  the  surface  to  guard  the  opening.  Replace  cover,  noting 
that  it  is  properly  seated,  upon  completion  of  work.  If  excava- 
tions are  made,  see  that  they  are  properly  fenced,  lighted  and 
guarded. 


308     UNDERGROUND  TRANSMISSION  AND  DISTRIBUTION 

GLOVES,  BOOTS,  ETC. 

When  working  on  any  cable  or  piece  of  apparatus,  wear  rubber 
gloves  and  rubber  boots,  and  before  beginning  work  satisfy  your- 
self that  these  are  in  good  condition.  Do  not  wear  boots  with 
nails  in  the  heels.  Use  a  dry  board  to  stand  on,  and  an  insulating 
barrier  around  live  parts  where  possible.  All  conducting  parts 
of  tools  or  appliances  that  need  not  be  exposed  must  be  insulated. 
Be  sure  your  tools  are  in  good  condition.  Never  leave  tools  lying 
around  loose  where  they  may  come  into  accidental  contact  with 
live  parts.  Keep  sleeves  down  and  avoid  contact  between  any 
part  of  your  body  and  live  cable  or  apparatus. 

BE  SURE  You  HAVE  THE  RIGHT  CABLE 

When  sent  out  to  do  any  work,  be  positive  you  understand 
exactly  what  you  are  to  do.  Be  sure  you  have  the  right  cable 
before  beginning  any  work.  If  tags  are  missing  or  if  from  any 
cause,  there  is  difficulty  in  locating  the  proper  cable,  report 
promptly  to  the  foreman  or  superintendent. 

LIVE  WORK 

Treat  every  cable  and  piece  of  apparatus  as  alive  until  you 
have  satisfied  yourself  that  it  is  dead  and  until  then  observe  all 
precautions. 

HIGH-VOLTAGE  WORK 

Do  not  work  on  live  high-tension  cable  or  apparatus,  without 
express  and  definite  orders  from  the  foreman  or  superintendent. 
Never  attempt  to  splice  a  high-voltage  cable  alive.  When  in- 
structed to  have  the  current  disconnected  before  beginning  work, 
make  certain  that  the  switchboard  attendant  understands  upon 
which  circuit  you  are  to  work  and  do  not  begin  until  he  tells  you 
the  circuit  is  dead.  As  soon  as  you  have  notified  the  station 
to  put  the  current  on,  consider  the  circuit  alive.  Make  certain 
that  no  other  workman  is  engaged  on  the  same  circuit  before 
having  current  connected. 

REPORT  DEFECTS 

Report  without  delay  to  the  foreman  or  superintendent  the 
presence  of  gas  or  water  in  manholes,  or  any  defect  or  unusual 
condition  you  may  observe. 


INDEX 


Agreement,  form  of  franchise,  24 
Arcing  ground  suppressor,  276 
Armored  cable,  94,  129 

cables,  jointing  of,  176 

services,  263 
Arresters,  lightning,  216 


B 


Balanced  system  of  protection,  278 
Block  distribution,  82 
Bond,  form  of  indemnity,  75 
Bonds,  drainage,  284 
Bonding  of  cables,  305 
Boxes,  junction,  252 

sectionalizing,  252 
Brooks  system,  6 
Built-in  system,  7,  88 
Bus  service,  258 


Cable  pulling  grips,  157 

reels,  120 

systems,  operation  of,  296 

testing  equipment,  237 

tunnels,  64 
Cables,  armored,  94,  129 

bonding  of,  305 

current    carrying    capacity    of, 
199 

diameter  and  length  of,  119,  124 

faults  in,  233 

fibre  core,  120 

general  data  on,  102-122 

heating  of,  228 

installation  of,  151-157 

location  of  faults  in,  233 

protection  of,  195 

sector,  126 


Cables,  specifications,  134, 135, 139- 
146| 

splicing  of,  168 

split  conductor,  278 

submarine,  129 

tagging  of,  297 

terminology,  102 

testing  of,  229 

transmission,  121 

types  of,  116 
Callender  system,  8 
Cambric  covered  cables,  177 
Choke  coils,  272 
Cleaning  manholes,  302 
Comb,  conduit,  45 
Concrete,  32 

manholes,  62 
Conduit  installation,  30 
Conducell  insulators,  187 
Conductors,  102-103 
Connections  to  overhead  lines,  209 
Construction,  early  forms  of,  5 

present  form  of,  17 
Contract,  form  of,  67 
Cooling  of  duct  lines,  205 
Copper,  properties,  104-105 

sleeves,  174 

Corrosion,  electrolytic,  281 
Costs,  construction,  76 
Cost  of  steel-taped  cable,  101 
Crompton  system,  7 
Gumming  duct,  13 
Current  carrying  capacity  of  cables, 
199 


Design  of  manholes,  54 
Development,  periods  of, 
Distribution,  block,  82 

holes,  63 

sidewalk,  84 


309 


310 


INDEX 


Distribution,  street,  81 

systems  of,  241 
Dorsett  conduit,  13 
Drainage  systems,  284 
Draw  rope,  160 
Dra wing-in  apparatus,  161 

systems,  11 
Duct  cleaners,  155 

fibre,  41 

lines,  routing  of,  86 

stone,  40 

tile,  34 
Ducts,  arrangement  of,  85 

choice  of,  153 

rodding  of,  154 

sealing  of,  47 

E 

Early  underground  systems,  5 
Edison  system,  4,  9 
Electrolysis,  281 

prevention  of,  290 

surveys,  293 


Failures,  records  of  cable,  300 
Fault  localizer,  274 
Faults,  location  of,  233 

locating  equipment,  237 
Fibre  core  cables,  120 

duct,  41 

Fireproofing  cables,  198 
Forms,  concrete  manhole,  62 
Franchise  agreement,  24 


Gas  in  conduit  systems,  47 
Graded  insulation,  114 
Grips  for  cable  pulling,  157 
Ground  suppressor,  276 
Grounded  neutral  systems,  277 


Heating  of  cables,  228 
of  duct  lines,  205 
of  manholes,  302 


High   tension    cable   specifications, 

146 

voltage  testing  of  cables,  240 
Holes,  distribution,  63 


Identification  of  cables,  297 
Installation  of  conduits,  30 
Insulating  compound,  183 

pipe  joints,  286 
Insulation,  graded,  114 

kinds  of,  105 

paper,  111 

rubber,  109 

varnished  cambric,  113 
Interior  conduit  system,  13 
Iron  clad  services,  263 


Jack,  pipe  forcing,  91 

reel,  151 
Jointing  material,  193 

of  cables,  168 
Junction  boxes,  252 

K 

Kennedy  system,  8 
L 

Lamp  standards,  concrete,  99 
Lead,  properties  of,  115 

sheath,  114 

sleeves,  weights  of,  173 
Lightning  arresters,  216 
Loop  test,  234 

M 

Mains,  secondary,  246 
Maintenance  of  cable  systems,  296- 

302 

Mandril,  36 
Manhole  covers,  50 

roof  construction,  50 

switches,  259 

waterproofing,  54 


INDEX 


311 


Manholes,  cleaning  of,  302 

concrete,  62 

construction  of,  46 

cost  of,  79 

design  of,  54 

distribution,  54 

heating  of,  302 

in  quicksand,  49 

transformer,  55 

transmission,  54 

types  of,  48 

ventilation  of,  225,  250 
Maps  of  conduit  systems,  19 
Materials,  selection  of,  30 
Merz    system   of  cable  protection, 

278 

Meter  protection,  263 
Mica  tube  joints,  186 
Moisture  in  cable  insulation,  149 
Multiple  tile  duct,  34 
Municipal  regulation,  23-27 

N 

Network  protector,  261 
Neutral,  grounding  of,  277 

O 

Obstructions,  20 

Oils,  impregnating,  111 

Operation  of  cables,  125 

of  cable  systems,  296-302 


Paper  cables,  jointing  of,  177 
ca'ble  specifications,  139 
insulation,  111 
tube  joints,  179 

Periodic  testing  of  cables,  240 

Permits,  21 

Pipe  forcing  jack,  91 

Plans     for     conduit     construction, 
19 

Pole  terminals,  209 

Potheads,  209 

Power  trucks,  164 

Present  forms  of  construction,  17 


Protecting  sheaths  against  electrol- 
ysis, 287 
Protection  of  cables,  195 

of  transmission  systems,  270 
Protective  pipe  coatings,  285 
Protector  on  A.  C.  networks,  261 


R 


Rating  of  cables,  199 
Reactance  coils,  272 
Records  of  cable  failures,  300 

installations,  296 
Reels,  cable,  120 
Reel  jack,  151 

Regulations,  municipal,  23-27 
Relays,  270 

Repairing  cable  failures,  233 
Right-of-way,  22 
Rodding  ducts,  154 
Rope  for  pulling  cables,  160 
Routing  of  duct  lines,  86 
Rubber  cable  specifications,  135 

covered  cable,  jointing  of,  176 

insulation,  109 
Rules,  safety,  306 

standardization,  228 


S 


Safety  devices,  217 

regulations,  306 
Sealing  of  ducts,  47 
Secondary  mains,  246 
Sectionalizing  boxes,  252 
Sector  cables,  126,  278 
Selective  fault  localizer,  274 
Service  bus,  258 

connections,  90 
Services,  protection  of,  263 
Sheath,  lead,  114 
Sheaves  for  cable  pulling,  164 
Sidewalk  distribution,  84 
Single  tile  duct,  34 
Slack  in  cables,  167 
Sleeve-filling  material,  183 
Sleeves,  copper,  174 

lead,  173 
Solid  system,  88 


312 


INDEX 


Specifications,  cable,  134,  135,  139- 
146 

conduit  and  manhole,  67 
Splicing  cables,  168 

equipment,  217 
Split  conductor  cables,  278 

core  transformer,  303 
Standardization  rules,  228 
Steel-pipe  systems,  14 

taped  cable,  94-100 

cost  of,  101 
Stone  duct,  40 
Street  distribution,  81 

lighting  cable,  97 
Submarine  cables,  129 
Subway  transformers,  248 
Suppressor,  arcing  ground,  276 
Surveys,  electrolysis,  293 
Switches,  oil,  259 

manhole,  259 


Tagging  of  cables,  297 
Temperature  of  cables,  228 
Terminal  blocks,  97 
Terminals,  pole,  209 
Terminology,  cable,  102 
Test  holes,  20 

voltages,  123 
Tests,  high  voltage,  240 

periodic,  240 


Testing  equipment,  237 

of  cables,  229 

for  live  cables,  223 
Tile  duct,  34 
Tools  for  splicing,  217 
Transformer  manholes,  55 

split  core,  303 

Transformers,  underground,  248 
Transmission  cables,  121 

systems,  protection  of,  270 
Trucks,  power,  164 
Tunnels,  cable,  64 


U 


Underground  transformers,  248 
Units,  electrical,  227 


Vacuum  joints,  188 
Varnished  cambric,  113 
Ventilation  of  manholes,  225,  250 
Voltages,  wroking  and  test,  123 

W 

Waterproofing  manholes,  54 

Webber  system,  13 

Winch,  cable  pulling,  161 

Wooden  duct,  14 

Wrought  iron  pipe  systems,  14 


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